Use the plugin name to set the active tool/display type(s)

Made active tool a slot, this can be used by extensions etc to
more seamlessly set default tools/display types after actions
are executed.

Change-Id: Ic1130c356b5147ff74eba758bcc92a59b58b2e74
Merge topic 'use-plugin-names' into master

59c7e21a Use the plugin name to set the active tool/display type(s)