2349: remove ------ from team language options

There's no need to include it -- Chosen handles the "empty selection" option.
2341: force moderated edits to go through the tasks panel

If we don't do this we can get strange things happening with review/approve
tasks.
Merge branch 'staging' into i-2341
added a few more selenium tests for non-deleted forked tasks, i2328
remove debug screenshot
update selenium tests for changed to edit subtitles button display i2341
2358: Don't crash when uploading translations from non-public languages

Changed it so that the form raises a ValidationError in this case,
instead of crashing when self.from_sv is None.

Changed it so the only valid choices for source translations are
public languages.  This matches the choices when you start the task in
the editor, so I think it's correct.
Fix for query to pull languages.

The previous one would have duplicates if we had multiple subtitle
versions.
Don't crash if a task has been deleted in TaskUploadForm
Merge pull request #166 from pculture/x-2358

X 2358
Merge branch 'i-2341' into staging
Merge branch 'i-2349' into staging
Merge pull request #169 from pculture/x-2344

X 2344
Merge pull request #170 from pculture/x-2328

2328: Don't delete in-progress/review/approve tasks on delete language
Merge pull request #171 from jdragojevic/wd-i2341

update selenium tests for changed to edit subtitles button display i2341
Merge pull request #172 from jdragojevic/wd-i2328

Wd i2328
skipping this for now
Merge pull request #173 from jdragojevic/wd-updates7

skipping this for now
2360: Update subtitle overlay as we type
2175: Fixed cursor positioning when clicking subtitle items