* localize the block and menu strings in the pen extension
* adds .tx/config to be able to push translations to transifex
* includes format-message to localize strings and extracting them.
* add setLocale function to VM to allow GUI to pass in locale data.
* refresh block definitions when the locale changes.
### Still to be decided
For now just extracting messages from the pen extension into their own file. We’ll need to decide if each category gets its own file, or group all the strings into one resource.
This informs webpack (say, in `scratch-gui`) about the web-targeted
build output so that it can resolve dependencies correctly. This fixes
build problems that became evident after merging #805.
This prevents generation of invalid XML due to characters like '<' or
'>' in fields' default values. Unfortunately the value comes back in its
escaped form, so there's still more work to be done.
When asked to load an extension, the Extension Manager starts up a new
Worker. That worker runs the message dispatch system as well as an
instance of the new `ExtensionWorker` class, which will load the desired
extension and register it with the extension system.
Extensions, placed in `./src/extensions/*.js`, are now processed by
Webpack as separate entry points and packed into an `extensions`
subdirectory in the output.
Still to do: query an extension's information, including the blocks it
provides, and register that information with the VM, GUI, etc.
The tests run using TinyWorker, which emulates web workers on Node.
There are quite a few quirks in that situation due to the differences
between Node and Webpack as well as the differences between TinyWorker
and real Web Workers.
The tests also exposed a few bugs in the dispatch system, which have now
been fixed. Most notably, if a method called through the dispatch system
throws an exception that exception will now be passed back to the
caller. Previously the exception would escape the dispatch system and
the caller would never hear any response at all.
Reverts #551
Pinning to `^0.1.0.prerelease.0` is not equivalent to `latest`, since has the effect of not installing the latest version on `npm install`, you have to also do `npm update`. This hurts us ergonomically on `npm install`, and doesn't help us since we already are releasing breaking changes on `prerelease`.
