Module can register action
Window adds this action to its menu
Clicking the menu item for the action has the expected result
But menu structure still needs work (everything is now put into one dropdown menu)
As a test implementation, this allows the TablesPage to open a CrudTab for a table/view without
the need for TablesPage, CrudTab and DatabaseWindow to know anything about each other.
in the direction of a plugin system.
DatabaseWindow now passes a Context to QueryTab and other pages that give those pages an
API for passing information up the system without knowing anything about the sytem.
