REST API Endpoints

[obenland]

Create REST API endpoints for the directory's theme.
Add additional endpoints to create language packs and notify GlotPress about importing strings.

[dd32]

In 3020:

Plugin Directory: Add a REST API endpoint which represents the full plugin data currently exposed through api.wordpress.org.
Although it's unlikely api.wordpress.org will run the API directly, this is a test to verify that all data we have on file is available.

See #1576

[dd32]

In 3021:

Plugin Directory: Correct a typo in [3020] and include trunk in the versions listing.

See #1576

[dd32]

In 3022:

Plugin Directory: Correct another typo in [3020], the post_excerpt is the short_description field..

See #1576

[obenland]

In 4484:

Plugin Directory: First pass at adding post meta to REST API.

We'll need to register our own rest api fields for more complex data
structures, namely objects and arrays of objects.

See #1576.