Apply syntax highlighting to fenced code blocks client-side

Instead of applying the syntax highlighting scheme class to these blocks
server-side, we use Javascript and Gon to apply the user's color scheme
(or the default) client-side.

This will make it easier to cache these blocks in the future because
they're no longer state-dependent.

See merge request !1203

Very similar to Gitlab::Theme, this contains all of the definitions for
our syntax highlighting schemes.

and request them each session. Pass these tokens to the project import data.

This prevents the need to encrypt these tokens and clear them in case they
expire or get revoked.

For example, if you deleted and re-created OAuth2 keys for Bitbucket, you would get
an Error 500 with no way to recover:

```
Started GET "/import/bitbucket/status" for x.x.x.x at 2015-08-07 05:24:10 +0000
Processing by Import::BitbucketController#status as HTML
Completed 500 Internal Server Error in 607ms (ActiveRecord: 2.3ms)

NameError (uninitialized constant Import::BitbucketController::Unauthorized):
  app/controllers/import/bitbucket_controller.rb:77:in `rescue in go_to_bitbucket_for_permissions'
  app/controllers/import/bitbucket_controller.rb:74:in `go_to_bitbucket_for_permissions'
  app/controllers/import/bitbucket_controller.rb:86:in `bitbucket_unauthorized'
```

Closes #1871

Reply by email

Fixes #1360.

It's far from done, but _it works_.

See merge request !1173