#555016 by Berdir | neriweaver, trupal218, BenK, nbz, archard, nilsja, kriskd, Liliplanet, yaz085, litwol, Feet, jaron: Added recipient types, allowing to send messages to roles and other recipient groups.

#315325 by nbz, litwol: Userblocking architecture + other fixes. Early commit to enable the developers to focus changes that need to happen rather than the whole new feature. This commit introduces number of bugs and inconsistent $form_values[author] setting (sometimes uid and sometimes object), that needs to be fixed. also fixed message previews (feature broken partially due to inconsistent $form_values[author] setting). some other fixes.