This patch renames `BaseClient::set_or_reload_session`
to `BaseClient::activate`, and `BaseClient::logged_in` to
`BaseClient::is_activated`.
The idea behind these renamings is to introduce a “state” for the
`BaseClient`: it is activated when is has a `SessionMeta`, has loaded
its data from the storages, and has an `OlmMachine`. Consequently, the
`logged_in` method is renamed `is_activated` for the symmetry. If one
wants to know if the client is logged in, it can use `is_activated`, or
also `MatrixAuth::logged_in`.
Ivan Enderlin
de615f2ffe