2163: don't create a new subtitle version when tasks are approved
Better layout for the html diff page

- Align the start of the 2 subtitle lists vertically.
- If a subtitle was inserted/deleted, then we insert whitespace in the
  other list. This way the subsequent lines still match up.
Merge pull request #140 from bendk/x-2163

2163: don't create a new subtitle version when tasks are approved
Merge pull request #141 from bendk/x-1582-pagelayout

Better layout for the html for the subtitles diff page
Redundant call is redundant.
2155: parents should be pulled from full(), not public()

When adding subtitle versions, parents need to be the latest version, even if it
happens to be deleted.
add some selenium tests for revisions / following
added a test for i2178
Added a bunch of tests for translation tasks.

Made tests use the test_factories module to create objects instead of
teamstestsutils.  Made default password "password" for users in
test_factories.

Fixed return value for Task._complete_subtitles().
Refactored code to simulate the editor widget for tests

Moved it into the tests module and tried to generalize it a bit.
Seems like other test code could definitely make use of this.
Made tests for translations.