Since we will introduce another type of plugin for the policy engine
we want to have each plugin type in separate directories.
We also have to adjust:
- plugin search directories
- po file location
- update paths for calls-doc target
introduce `calls_sip_media_manager_get_capabilities ()` which takes
a GList of MediaCodecInfo's as input to generate a SDP message.
If using in an SDP answer we simply feed it a list of the common codecs
as gathered from the SDP offer.
static capabilities are now supporting multiple codecs and generate correct SDP
messages. This only relates to SDP offers. When we are answering an offer we
must take the offer from the other party into account when creating the answer.
Hence why we differentiate between "static" and "dynamic" (not implemented yet)
capability strings.