CHUI-707: "Chat" toolbar button stop flashing after setting toolbar buttons view to "Icons only": save/restore flashing states

Added messages, for now they're displayed in two cases:
1) no log entries, logging disabled
2) no log entries, logging enabled
Case when there are existing log entries and
logging is disabled is still under discussion

CHUI-732 : Fixed! Do not iterate through selection while modufying it at the same time, use a temp set.

CHUI-691: Now when an estate message is received while in DND mode, a toast notification will appear.

CHUI-720 FIX User can open "Add friend" by pressing on a line in context menu for user that already is friend
Added check for getVisible() and getEnabled() before passing along handleMouseDown() and handleMouseUp() callbacks to other menu items in LLMenuItemSeparatorGL

CHUI-689: When DND mode is enabled, making a direct delivery purchase results in an IM message from '(Nobody)'. Solution: Fixed a problem in process_improved_im that would falsy use system messages while in DND mode as an IM from a user. Also made it so that while in DND mode, SystemMessages and message with a high or greater priority are shown to the user as toasts (before a notification chiclet would just appear without the toast).

CHUI-675 FIX You can select multiple users in people floater but can only drag and drop one name to conversation
Moved drag and drop start in LLAvatarListItem instead of LLAvatarList, and made LLFloaterIMSession handle multiple dropped participants correctly

CHUI-711 FIXED Load logs from file only once to avoid duplicating. This will also solve problem with chui-710.

CHUI-704 (Entry in 'Conversation Log' floater with your avatar's name appears, after ejecting any member from group)

CHUI-704 (Entry in 'Conversation Log' floater with your avatar's name appears, after ejecting any member from group)

CHUI-647 FIX "Conversations" floater is not opened when user wants to share something via "Conversation log" floater
Added call to show conversations floater in LLAvatarActions::share

CHUI-436 : Fixed : Do not skip yourself or group chat when checked Only friends and groups can call or IM me pref.