Fixed an issue which caused the schema to only get fetched for geogit layers.
The feature edit dialog will now respect the nillable schema property and will not let the user save null or an empty string to a field marked as non-nillable
Added billable support to the table view and fixed an issue that was preventing the table from saving edits
Added a 'null' option to the drop down inputs in the table.  Changed the UI to accommodate this and be more consistent with the rest of MapLoom
Added Nillable support to the diff panel.  Also fixed a couple rebased related issues.  There is still an issue with photos in the tableview.
Resolved issue with table saving and removed photo attributes from the table.
Refactored the table's save function to save all features at once as a single commit.  Disabled filtering while the table is being edited to prevent issues.  The table can still be filtered before starting an edit.