Task Group widget and modal content.

This pull request provides the following functionality:<br><br>   Task group widget updated with functioning objects mapper and tasks mapper with lookup autocomplete<br>   Task groups properly mapped to objects and tasks<br>   Autocomplete refactored to allow subclassing through jQuery-UI widget factory,<br>   made subclass that filters on an object's mapping;<br>   Drag handles for reordering tasks.<br>   Locking/unlocking of task order implemented<br>   Enabling confirm delete modal (and delete) from TaskGroup tree view Fixed up task listing and re-tasking directly in list, enabled task group deletion, disabled handles and trash icon when task order locked.<br>  Arbitrary-precision string math functions for determining task_group_task sort order