Reuse existing code
Fixed search form action URL

This didn't generate proper URLs when the user was in a context of the
file/dir browser.
Simplified code, handle the situation with no args
Added support for all sorts of directories
Added convenience `get_translate_url` methods
Use `get_path_obj`
Added manager method to retrieve units below a given path

Works for any `pootle_path` and does permission checking for the user
attached to the given `profile`.
Use `get_for_path` to support arbitrary paths
No need to retrieve a `path_obj` that won't be used
Differentiate between `Directory` and other objects

Also removed the IndexError check since the decorator is meant to be used
along with `get_path_obj`.
Reordered import
Improved readability
Implemented global search

This commit adds the pieces for having translation editors at the root of
the server, at projects across languages, and at languages across
projects.

Fixes bug 2719
Removed lookup backends.
Cleanup: removed cruft
Group by `pootle_path` for uniqueness

Units from different stores could be grouped together otherwise.
Display file delimiter rows in the editor

Fixes bug 2946.
Cleanup: removed exceptional handling for SQLite
Ignore empty path parts
Revert "Ignore empty path parts"

This reverts commit ae05ed7c2235dc8a2c2c5811d564deda57059b0e.

This breaks project overview for me:

  Traceback (most recent call last):
    ...

    File "pootle/core/url_helpers.py", line 49, in split_pootle_path
      ctx = parts[2]
  IndexError: list index out of range