Split the dialer and the observer logic for better events handling

As proposed by @bshah, the architecture changes similar to spacebar#2 (closed) and ubports telephony-service+dialer-app approach are needed.

Currently the approver is a daemon, and the dialer app is a client, so not all channels get passed to the client.

The idea is to split the logic into:

• Observer:

  • Keep a record of calls/history
  • Enable audio channels when needed

• Approver:

  • Show notification and of-course dispatch channels to the client

• Dialer:

  • Provide general UI

It's mostly code is already there, just needs splitting into 2 binaries: i.e approver is the same and the dialer client code needs splitting in a separate observer.