This includes the following changes:
- Introduce a `providers` hash table to keep track of multiple CallProvider's
and remove the `provider` member
- Remove `calls_manager_get_provider()` and `calls_manager_set_provider()`
in favour of `calls_manager_add_provider()`, `calls_manager_remove_provider()`
and `calls_manager_has_provider()`
- Introduce a `origins` GListStore to keep track of available origins.
`origins` is updated in `items_changed_cb()` when the origins of any
CallsProvider are updated.
- Adapt to changes with respect to `calls_manager_get_origins()`.
- Introduce `origins_by_protocol` hash table to keep track of available origins
per protocol.
- Adjust tests
- We temporarily break country code lookup which was handled previously
with the "default-origin" mechanism. We will add it back to the CallsSettings
class which will provide a better application-wide mechanism.
0b2f146053