[Sprint/InterestingIguana](chore): Consistent messenger dockpane styles and ribbon behavior

Made the dockpane borders/shadows the same for userlist and conversations. For both userlist and conversations, ribbon opens when you click its button even when the dockpane is closed. Action tab buttons and icons change color on hover. Encryption text is horizontally aligned with dockpane tab title.

Relates to #1484 (closed)