[bug 916800] Switch from is_superuser to is_manager.
[fix bug 888157] Correctly handle translatable strings with variables.
[fix bug 989342] Allow Managers to delete groups.
Merge pull request #880 from glogiotatidis/888157

[fix bug 888157] Correctly handle translatable strings with variables.
Merge pull request #870 from glogiotatidis/916800

[bug 916800] and [fix bug 989342]
Add localization documentation.

Also cleanup documentation.
Merge pull request #886 from glogiotatidis/docs-upgrade

Add localization documentation.
Change UserFactory to create vouched users by default.

Since the most common test scenario requires vouched users to work, I
switched UserFactory to vouch users by default. Also added parameter
'vouched' to easily explicitly control the vouch status.
Don't need to force ElasticSearch update after UserFactory.create().