Ref: #284
This allows to see if a widget is stacked for example. It uses getters instead of exposing the properties directly, which should be made readonly then probably (which has drawbacks according to [1]). 1: http://lua-users.org/wiki/ReadOnlyTables Closes https://github.com/awesomeWM/awesome/pull/284.
Signed-off-b: Julian Wollrath <jwollrath@web.de>