Deleting a filter associated with a board, deletes a board with no warning

If a filter is used as the definition of a board, and that filter is deleted, the board is automatically deleted. There is no warning to the user about such an action being done.

There is also no way to currently know what filters are being used to as the source for a board.

We should be either warned or the board not be deleted. It doesn't contain data or defaults to the project...but, I did not expect the board to be removed.