Adds possibility to build extension files (Chrome and Safari) from
command line.
To run from the project directory:
python tools/build.py [meta]
If the optional `meta` argument is set, then only the manifest and
language files are uptated.
Without that everything is being built (extension files too) into the
`dist/build/version_number` folder.
For Chrome there will be two files, a crx, and a .zip file which
includes the key.pem private key (so this must not be shared,
it's just a bit help for publishing it to the Chrome Web Store).
Beside the extension files, update-files are generated too (for self
hosting - Safari needs it).
Chrome has getManifest(), Safari doesn't have anything, Firefox has an
asynchronous API...
So, instead of using extension APIs, store the common informations
(extension name, version, homepage url) in a file (vapi-appinfo.js), which
can be included when it's needed (its data will be available at vAPI.app.____).
The file's content is updated each time the extension is being built, so
it shouldn't be modified manually.
