Many improvements to pbx-calls.lua:

Many improvements to pbx-calls.lua:

1) Now trimming whitespace from all input before checking validity (of extensions, users, providers).
2) Now building valid outdoing providers and valid users array while rendering page since we're going
   through all providers and users anyway to display the page (saves cycles).
3) Now not displaying internal naming scheme of providers to users, but what they expect (us#erin%fo@host.org).
   Before we used to show us_erin_fo@host_org, and it was ugly and needed explanations.
4) Got rid of some no-longer-needed functions due to improvements mentioned in (2).
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