[sldev] Jira: Turn the SL GUI classes into a standalone framework

[Lawson English]

 https://jira.secondlife.com/browse/MISC-621 factor the SL GUI framework 
into its own separate library that isn't slaved to viewer development.

There are a lot of upsides to this. I mention some in the jira. No doubt 
there are many downsides. These also should be discussed primarly on the 
jira.

Thanks for reading this,

Lawson English