Initial commit for categories. Schema/Model changes

* Added support for category in boards schema/model
* Outline for two new board methods: updateCategories and allCategories
Implemented allCategories, updateCategories and categoryDeleteBoard

* Still a work in progress.
* Need to call categoryDeleteBoard upon board.purge
* Need to implement tests for new board methods
Updated Tests and implemented fixes for allCategories/updateCategories

* All test should be passing, categories should now be supported