Fixes #105

Due to a latency issue with btrfs, it sometimes returns errorcode = 19. The fix
is hopefully temporary where if list operations pool for upto 30 seconds, it
should work.
Merge branch 'master' into issue#105
Merge pull request #254 from schakrava/issue#105

Issue#105
Replication

Add views and templates for replication task list and new task creation
Enable / disable for replication tasks
Display replica trail for replicas
Update replication model to save all state transitions properly.
Add pagination support for replica trail
Update replication scheduler and sender for the updated data model
Replication

Add start, end, duration, status columns for replica trails
Pagination for replica trails
Update replication model to store user_tag information
Provide replicas and trail in a sorted(descending ids) order by default
Update frontend templates so user can click on target appliance to go to it's
ui on a new page
Change the user_tag to task_name to comply with frontend
Display replica name
Merge branch 'master' of github.com:schakrava/rockstor-core