mv git user/mail checking to beginning of collection.sync view
webui.tasks.DebugTask -> FileAddDebugTask

This is used specifically for file uploads, and we need a
DebugTask for collection_sync.
farm out collection sync to Celery task

- webui.tasks.collection_sync function that calls commands.sync.
- UI notification messages.
- DebugTask method that unlocaks collection after task completes.
- Mod session_tasks to allow for non-file-add tasks.
slightly better comments for webui.tasks.session_tasks
Merge branch 'master' into 059-sync-celery