Enable translation of plural forms

Issue #238
Remove TranslationStringFactory

TranslationFacotry is only useful for non-plural forms. It only defines a
default domain for a particular string, and it's easily replacable with
a `setdefault`

https://github.com/Pylons/translationstring/blob/master/translationstring/__init__.py#L131

Issue #238
Update l10n source files
Don't load imagery in JOSM if not available
Check for user name change. First round.
With tests (by mocking OSM API responses)
Don't update user in DB if username didn't change
Consistant function names
Adding support for code block (for markdown fields). Fixes #305.
Add support for closed linestrings by converting them to polygons. Fixes #246.
Removing extra node. + indentation
Merge pull request #299 from pgiraud/missing_imagery_josm

Don't load imagery in JOSM if not available
Use joinedload to get project translations
Fixing tests
Reduce number of calls to authenticated_userid in home page
Join load author and area to reduce number of queries
More consistency
Lazy is select by default
Merge pull request #313 from pgiraud/home_perfs

Reduce number of queries in home page
Merge pull request #309 from pgiraud/export_osm_closed_way

Export to OSM cleanup.