add call completion extensions
use a single "toggle" extension for call completion
add ccss options in sip.conf

Tests are refactored so that they don't need to be modified each time a new option is added
simplify condition
add ccss options in sip.conf
only use minimal set of ccss options
generate ccss_options once instead of once per user
add some assertions to ccss unit tests
Merge branch '5141-ccss'