Add comments, fix some java docs, delete unused imports. Reduce warnings from CodePro.

Change-Id: I104e602687940d7cbbe36d0919b427dd74b8c07a
Refactor buckets a little and remove the archive bucket stuff

Making buckets use MVP is all but a requirement for advanced features like drag and drop.

The archive is also no longer a bucket, so it's removed.

Change-Id: I9040fcf0e9b9c937394f6e4961ea2e8e7f7b3f0d
Refactor MiniTaskView to use models instead of raw data

Similar to the last commit, this is a really tiny change that makes
new features way less difficult to add.

Change-Id: I03f85b8f9033fc0960cd07b9dea0421b49612cc5
Add basic drag and drop functionality

Tasks can be dragged and dropped between buckets.  They cannot be
reordered yet and there's very minimal visual feedback.

Change-Id: I74e84aafb0cce5f5c5d9076bd19bd630f0b0bb36