SH-2541 Fix for speckles on avatar on some cards -- don't use "maximum_alpha" for alpha tests in shaders as it was always being set to 1.0 anyway.

SH-2546 Fix for black avatars and terrain on GF Go 7800 (use vec3 instead of float on varying parameters).

EXP-1479 FIX Chat history does not open when selecting toggle on chat floater and issue with minimizing and opening chat floater

EXP-1458 FIX Chat text entry bar does not have focus when chat floater is opened while chat history is toggled open

EXP-1461 FIX Incoming Nearby chat not visible in chat toasts/bubbles to user when chat window is minimized with chat history opened
made minimizing and unminimizing nearby chat floater do the right thing

EXP-1461 FIX Incoming Nearby chat not visible in chat toasts/bubbles to user when chat window is minimized with chat history opened

EXP-1417 FIXED (Docked Notifications window tears off from the dock icon when deleting notifications one by one)

- Changed LLSysWellWindow::reshapeWindow() so that the floater decreases from bottom to top, without changing top coordinate.

- Force dock control repositioning in case floater rect changed.

EXP-1469 FIX -- Changing toolbar from "icons only" to "icons with text" while incoming/outgoing call floater is open causes crash on mac

* Updated LLToolBar to call remove and add on all buttons when rebuilding the toolbar.

EXP-1398 FIX -- Viewer Crash when moving Speak button from bottom toolbar to side toolbar with call request dialog active on Mac

* Added "on button removed" callback for toolbars.
* Changed docking on incoming and outgoing call floaters to be undocked when "speak" button removed.

Reviewed by Leyla.

made sessionsettings pref not persistent

Adding back code that was accidentally removed in changeset ff333a95d1aa.