[voicecall] Fix uncallable DBus function.

Methods marked as Q_INVOKABLE are not callable over the DBus interface.
Make resetCallDurationCounters() a slot like all the other DBus
methods.
[voicecall] voicecall-manager.service uses new boot targets

Signed-off-by: Pekka Lundstrom <pekka.lundstrom@jollamobile.com>
[voicecall] Add missing providers.pro
Merge pull request #17 from amccarthy/master

[voicecall] Fix uncallable DBus function.
Merge branch 'master' of github.com:nemomobile/voicecall
Merge pull request #18 from plundstr/master

voicecall-manager.service uses new boot targets
[voicecall] Remove a slot that doesn't do anything.