Fixes and Feature addition.

* Users can now add and delete categories.

* Added "none category" to category selection on item create/edit

* Fixed bug where sorting would break if user list was only one item long (discovered during feature review)

* Fixed bug where interface would edit the most recent Item instead of creating a new one. (discovered during feature review)

* Fixed bug where categories listings (dropdown and table) would relist instead of update.
Changed location of version and user agent constants to avoid update problems.
updates to Readme file
Merge remote-tracking branch 'upstream/master'