SH-3126 : Use correct unspecified ending byte range for all curl request when fetching files to the end.

For SH-3121: collect time of reloading all textures from cache and through HTTP when all objects loading are done.

As a viewer architect, I would like to understand how fast each of the components of the texture pipeline can run in isolation

Reviewed by Ted.

Move phase tracking to its own set of classes inside LLViewerStats - simplifies llvoavatar and allows adding such tracking to classes that live outside the avatar lifetime

Notification handlers now use LLHandles to screen channels.

Fixed boost trackable objects usage.