Closes #95

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* Covers parts of these issues: GUI layout panes (#69), sprite libraries (#12), import buttons (#64), menu bar (#67), and sprite info area (#53)

~ Refactored layout pane structure by removing `display: flex` from `.box`, by default. Declaring flex instead only where specifically needed. This helped fix layout quirks, and should help us avoid hard to find issues related to nested flex boxes

~ Added descriptive classnames to boxes/containers/wrappers. Moved more padding, margins + layout into these wrappers to help with component reusability.

~ Set up a spacer unit variable inside `gui.css`, to start keeping consistent padding, margins and rounded corners between panes. Used [CSS/PostCSS Modules](https://github.com/css-modules/postcss-modules-values) to avoid SCSS dependency.

~ Refactored inline styles from JSX, into CSS files. 2 reasons: a) prepping for reuse of CSS Module variables. b) Feels easier to debug complex flex layouts when all the styles are in one place vs JS/HTML/CSS syntax mixed together

~ Added menu bar into layout via new component, and sprite info header in sprite selector pane, with stubs for the labels + forms. Sprite items are correctly scrolling, while leaving the header fixed, in Chrome. Mostly working in FFx. Not working in Safari, IE yet.

~ Style pass on library modal

~ Experimenting with a few different transition styles: Logo in menu bar, sprite library items, Add buttons.

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Improves performance by comparing sprite info values (rather than object identities), and by excluding irrelevant data from this comparison.

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The previous method of configuring the port number was not cross-platform.  Resolves #20

The inline css method gives us nothing that CSS modules can't give us. This puts the project more in line with the way www works, and makes CSS actually readable.

Using class names gives us full control of the modal styles.

In preparation to split the sprites from the stage, start managing the target list state in a single place.

This removed our vendor files before. Prevent anything else from happening in the future

After doing this, new rules began applying for some reason:

`eol-last` only began taking the 'always' parameter as of 3.6.0, so I needed to update eslint.
`no-unused-var` started warning about process.env after updating the config structure
`comma-dangle` decided to start working, maybe because of the upgrade to eslint?  Autofixed with --fix

Includes rules missed in the first pass of eslint rules

Previously eslint ignored .jsx files :|

When the package is installed as a dependency, it should warn the installer that React is a peerDependency.  When installed this way, the devDependencies won't be installed, so only one version of React will be present. However when it's installed as a standalone project, React should be installed automatically as a devDependency.

I think this gives us the best of both worlds — simple development setup as well as supporting usage as an installed package.

Makes local deployment easier

So that you can adjust them without redefining the entire GUI.
Also allow adjusting props passed to GUIComponent.

`npm update` does what we want and is less hacky than removing the packages entirely first.  Specify latest as the version so we always get the latest version even though I erroneously installed scratch-blocks@0.1.0.

Use fewer refs, these had weird behavior that caused the order of components to matter.
Attach events eagerly, as soon as the necessary objects are available.
Make VMManager an actual class instantiated with a VM so we don't have to pass it to every method.
Use bindAll everywhere for convenience.

Once another project uses this package, these should become peerDependencies.  Until then install automatically.

While doing so:
- Use ProjectLoader for loading projects
- Stop using loadEmptyProject and supply empty project data
- Move project loading to App, GUI now receives data (as a string - the vm should receive an object eventually)
- Add logging