Uses new version of scratch-l10n.

* removed anything that was made redundant by scratch-l10n.
* updated a string that wasn’t following conventions
* added .tx/config so developers can start updating Transifex when there are new strings

Changed existing string ids to use the convention `<repo>.<component>.<identifier>`

To prevent loading scratch-blocks default toolbox

Alphabetize all the things

To show the "Add Extension" button, you must now add `?extensions` to
the URL used to load the GUI.

Also, delete `static-blocks.xml` which shouldn't have been added in the
first place.