Disable the add/remove column buttons when they are not allowed to be used. Removed the removing of the remove column button when only one column is left.

There is one bug with this stuff, caused because the new columns returned have the incorrect columnsN class. If all but one column is removed, then a column added to the left hand side, then you try adding a column to the right hand side, a javascript error will occur. This will be fixed when the correct data is sent back from the server.