Draft: Auto swap calls on hangup if holding

This patch adds a via to swap the calls when we finish a call, and have calls holding, to automatically swap to the call and release the active one. Currently, when the active is hanged up, the second keeps on hold, requiring the user to press the pause button to resume the holding one.

Signed-off-by: José Pekkarinen jose.pekkarinen@foxhound.fi