UC-258 - emergency dialing feature

    In sipXconfig:
    - ERL table with possibility to add locations and ELINs
    - Users and phones linked to ERLs
    REST API to:
    - save/update ERLs
    - link users to ERL

    UC-1374: New proxy plugin that rewrites from uri for emergency calling if an e911 line identifier is configured for the caller.
    UC-1373: Alarm info generated by PROXY on emergency calls contains ERL info