Add a new Identity type with the required methods so that now the board
types (Card, Status and soon Tag) can automatically satisfy the BoltItem
interface.
Remove the original 'Write' function from the db package and rename the
'WriteMany' function to 'Write' as it can already write one or many Bolt
items to the database.
Also update the test suites and add more coverage in the board package.
Add support for deleting status columns. If a column is not empty then
it will not be deleted and the user will see an error message in the
status bar.
Part of apollo/pelican#24
This commit adds support for creating new status columns. When the user
is in the 'board edit' mode, they can press the 'c' key to create a new
column. When a new column is created it automatically assumes the last
position on the board. We will add support later on to allow the user to
re-arrange the columns on the board.
Part of apollo/pelican#22
