Declare optional arguments on `ABCDatabase.*_access` methods

[flongford]

Not all of the The ABCDatabase.grant_access and ABCDatabase.revoke_access method arguments appear to be required.

simphony-remote/remoteappmanager/db/interfaces.py

Lines 208 to 209 in 510430b

	def grant_access(self, app_name, user_name, app_license,
	allow_home, allow_view, volume, allow_startup_data):

simphony-remote/remoteappmanager/db/interfaces.py

Lines 251 to 252 in 510430b

	def revoke_access(self, app_name, user_name, app_license,
	allow_home, allow_view, volume, allow_startup_data):

In fact all of them except app_name and user_name could probably be made optional with given defaults, since our implementations already expect to handle falsy values anyway.