MAINT-4009: Ensuring that the spare browser media source is cleaned up with the LLViewerMedia class.

MAINT-4009: Patching a small memory leak for when menu items were being created before the viewer window initialization had created the menu holder.  Also, added llasserts in other cases when referencing the menu holder to ensure the holder is non-null.

MAINT-4009: Patching the memory leak occurring from the info icons that appear when hovering over a chat history item.

MAINT-4009: Patching the memory leak occurring in the scenario where avatar icon was being created, but the tab container did not have a button to accept the gieven icon.

MAINT-4009: Patching the memory leak occurring in the scenario where toast panels were being created, but the screen channel were deciding not to display the given toasts.

MAINT-4009: Patching the LLTabContainer that was leaking some child views and their associated llimage allocations.

MAINT-4009: Patching another memory leak in LLBadgeOwner that indirectly was also causing leaks in llimage.

MAINT-4009: Ensuring that the pick mask for the LLImageGL is always properly freed during its cleanup method.

MAINT-4009: Converting the Globals class within llerror to be derived from LLSingleton so that it may be cleaned up properly on app exit.

MAINT-4009: Cleaning up some statically allocated memory in a LLVolumeGeometryManager method that was never freed.