Wrap each person within <maintainer/>

He's been the most active contributor recently.

Calls can't tell the difference between no SIM and no modem
atm.

Closes: #159, #152

Othewise we overflow the window. Center it too.

Added feedbackd to the Flatpak manifest, so that Calls builds again.

Fixes #164.

These have an empty string which leads to

    Error parsing phone number `': Keine Telefonnumme

For some locales, the buttons' labels can be quite long, making the
window wider than the display.

Using a line wrap will solve this issue when there wouldn't be shorter
translation alternatives. This requires reducing the encryption indicator's
margins so the window height doesn't grow beyond the available display size.

They can't be called back, we don't have a number

See: #144

If no number is present use `Anonymous caller` instead of an
empty label in the call history.

See: #144

* src/calls-manager.h: Add lookup function to header
* src/calls-manager.c: Implement lookup function to be used for the call
  history, call notifier and call display
* src/calls-call-holder.c: Use calls_manager_get_contact_name ()
* src/calls-notifier.c: Use calls_manager_get_contact_name ()

Since passing a CallsContacts pointer down to every class it needs, started to
become laborous - especially since the intermediates classes don't need
the reference themselves - it was made a singleton

* src/calls-contacts.c: Added calls_contacts_get_default () function and
  removed calls_contacts_new ()
* src/calls-contacts.h: Added _get_default () prototype and removed the
  _new () prototype
* src/calls-application.c: Use calls_contacts_get_default () now
* src/calls-history-box.c: Removed self->contacts completely
* src/calls-history-box.h: Got rid of CallsContacts argument in _new()
* src/calls-main-window.c: Removed self->contacts completely
* src/calls-main-window.h: Got rid of CallsContacts argument in _new()
* src/calls-call-record-row.c: Use calls_contacts_get_default () now
* src/calls-call-record-row.h: Got rid of CallsContacts argument in
  _new()
* src/calls-call-holder.c: Use calls_contacts_get_default () now
* src/calls-call-holder.h: Got rid of CallsContacts argument in _new()
* src/calls-call-window.c: Removed self->contacts completely
* src/calls-call-window.h: Got rid of CallsContacts argument in _new()
* src/calls-notifier.c: Use calls_contacts_get_default () now
* src/calls-notifier.h: Got rid of CallsContacts argument in _new()