The use of an "override" prop that allowed the preview modal to be hidden without actually changing the redux state was causing a problem where the block editors where not closing when modals were opening. That is because it relied on the modal reducer being accurate.

I defaulted the preview state to false to make it simpler to consume the GUI, as www will not want the preview info to be true. I made it true in the playground instead.

This fixes https://github.com/LLK/scratch-gui/issues/3710

stripped title handling from sb file uploader
updated more projectState related names
simplified hash-parser-hoc logic slightly

load new project, both json and title; set title on file load; draft of code to fetch title from api

Add `?locale=<localecode>` to load in a new langage.
Add `?enable=language` to enable the language selector
Or combine the two: `?enable=language&locale=<localecode>`
Still accepts a hash, but requires that the hash be a sequence of digits.

Added new locales reducer to gui:
- initializes default  react-intl/localeData
- initializes default locale messages for all locales
- default locale is ‘en’ (can be overridden by URL)

Removed dependency on react-intl-redux, added ConnectedIntlProvider (uses correct locale messages from redux based on current locale)

- better split of hash-parser/project-loader unit tests.

The project loader that is exported with GUI just expects to be passed projectId as a prop, and it manages loading project data.

The part of the project loader that watches for URL hash changes for the playground is a new HOC that is only used in the various playground examples.