sbc b/f: handle rejected offer
core: new callback when UAC/UAS transaction is finished
sbc: added support for re-trying failed re-INVITEs

... for few scenarios only for now (local hold/unhold request, local reINVITE)
sbc: make timer for re-trying upon 491 reply configurable
Merge branch kubartv/error_recovery

Conflicts:
	core/AmBasicSipDialog.cpp