Give support to custom actions without image

+ Those actions will not appear in the legend.
+ Added some devel doc to EBox::Types::MultiStateAction class
Update copyright end
Merge pull request #938 from Zentyal/ejhernandez/custom-actions-no-img

Give support to custom actions without image
fixed wrong changelog merge
Merge branch 'master' into ejhernandez/promote-demote-ha

Conflicts:
	main/core/ChangeLog