906859-import-messages - cleaned up error messages for both import and delete manifest

Minitest is skipped until non-private manifests can be created to excercise the code and be checked into git
Intial commit of filters functionality
Added nosetests for cli calls
Filter model tweaks based on PR suggestions
Removed an unused file
Updated the show call to info to be consistent
Changed couple of variable name as recommended in PR 1708
Removed unused import  statements
Added a todo comment as recommended in PR 1708
removed unnecessary to_json calls as suggested in PR 1708
Removed some trailing spaces in both py and rb files
Removed unnecessary commented lines
Removed trailing spaces
Making changes to keep pylint happy
renamed filter to content_filter when the file gets imported to help with pylint
Updated copyright years
Addded minitests  for filter model
Removing a trailing white space
Merge pull request #1708 from parthaa/new-filter-stuff

Initial filters work
Added tests related to filter_controller
(cherry picked from commit 5b1964d4245ed60e7b55ff873058270be672876f)