Fix issue #24

The P2 update site URL to mylyn was wrong.
Fix for #26.

The TaskAttribute.TASK_KIND property is now set to the redmine tracker
name.
Merge pull request #25 from giamma/master

Fixes a couple of issues (one I already merged, the other one is to do with task types)
Spinner is needlessly overscoped
Make Estimated Hours into a nullable
Fractional values are now persisted, and zero is treated as null
Merge pull request #39 from awilkins/estimated-time

Estimated time fixes