Add option for Horizontal buttons on Contacts floater.

Adds Use horizontal buttons for contacts floater (needs restart) to Vanity Preferences.
Adds ContactsUseHorizontalButtons.
Adds FloaterContactsHorizRect for saving horizontal contacts rect.
Adds panel_friends_horiz.xml, panel_group_horiz.xml, and floater_my_friends_horiz.xml

Also corrects string value for FloaterContactsRect
Split off certain preferences into new Adv. Chat subtab Chat UI

From Text Chat: Disallow communicate shortcut opening detached friends list
From Vanity: Use horizontal buttons for contacts floater (needs restart)
The rest were in Chat/IM of Vanity.
Optionally, have IM buttons on the same line as the person's name.

Adds UseConciseIMButtons.
Adds floater_instant_message_concisebuttons.xml
Adds Have buttons on the same line as name for IMs (Affects new IMs) checkbox to Adv. Chat's Chat UI tab.