In the case of errors depending on network input (i.e. not programming
logic errors), we should report errors but not abort the application.
Assertions should be used to validate and document programmer
assumptions. Moreover, if assertions are deactivated at build-time, we
don't want our application to crash.

This reverts commit 097dd607.
Config file and history file restoration work fine without breaking make
distcheck.

This breaks make distcheck, and hides serialization regressions.

Also added whitespace checking pre-commit hook when autogen.sh is called.

No need to represent DTMF with an enum

This reverts commit a4256fcb, reversing
changes made to aa2dd717.

Whenever we hangup or our peer hangs up a call, an entry is added to the history
(in memory). When the daemon exits, it will save the history
automatically.

This way we only have one representation of the history in memory
instead of 2, and we don't need a ConfigTree for this, standard streams are
sufficient.

Clients still need to be updated.

History saving still has to be updated.

This will replace the existing getHistory dbus method.