Unify source setting code -consistantly set system states for each source

[pitts-mo]

I had noticed inconsistency with source behaviors that depend on how the source state was entered. These discrepancies were primarily observed while comparing audio behavior between booting to source vs menu switch to source.

Quickly looking at the code I suspect these places contain code for consolidation:
/src/ui/page_source.c
/src/core/main.c
/src/core/app_state.c

It seems to me that primarily elements from page_source.c should be consolidated under app_state.c (?) so that a single routine would be utilized to consistently set all element states for each of the goggle sources regardless of where/when determination to enter source state was made.

More info:
I had noticed this issue in regard to audio handling over a year ago and I suspect resolving this issue may improve the ability to resolve some of the other consistency failures users have reported. Here are a few prior audio specific issues I suspect to be related:
#115
#328
#372