Restore some lost navbar styling

Fixes #3216
Hide the sidebar contents when closed

Fixes #3268
Re-add an argument that disappeared

Fixes #3271
Filter only on enabled() where relevant

Fixes #3270 and should close off #3248 as well. Thanks, @julen!
Store: Use a fields whitelist instead of blacklist for UnitForm

Also see evernote/pootle@0d730852d9ec8e650779f9a46dfa06860e986c21
Django 1.6: removed `UnitStateField` field's validation step

It has been removed because in Django 1.6 now that's part of the
`BooleanField` field's `validate()` method, which is called in the field's
`clean()`.
Django 1.6: be explicit about the fields included in ModelForms
Unit: forbid overwriting source texts from the web interface

Overwriting source texts in this context is undesired, which ended up in
mangled DB content because of evernote/pootle#278.

The reasoning behind allowing to edit source texts can be explained with
the fact that terminology units have been sharing the editing/validating
form with regular units. It's not the case anymore — these are very
different contexts with different use-cases.
latest_change_id: Fix a stdout.write call

Fixes #3272
check_names: Add isfuzzy check name

Fixes a crash on custom-mlo when looking for check_names["isfuzzy"]
Core: Sync .gitignore with core
travis: Print Python version as well
Core: Sync file headers and styles
Cleanup: use Django's own staticfiles' template tag

No point in duplicating functionality here.
Try hard not to break delete_path_obj()

Safely fixes issue #3274
Reimplement User.is_staff on top of is_superuser

Fixes issues with the django admin
Use content_type keyword argument instead of mimetype

DeprecationWarning: Using mimetype keyword argument is deprecated, use content_type instead
Underscore.js: upgraded to 1.6
Cleanup: moved BB-related libs to `vendor/backbone/`
Bump Django requirement to 1.6.5