Replace lager with built-in new logging API

Replace lager with built-in new logging API

This change requires Erlang/OTP-21.0 or higher.
The commit also deprecates the following options:
  - log_rotate_date
  - log_rate_limit

Furthermore, these options have no effect. The logger now fully
relies on log_rotate_size, that cannot be 0 anymore.

The loglevel option now accepts levels in literal formats.
Those are: none, emergency, alert, critical, error, warning, notice, info, debug.
Old integer values (0-5) are still supported and automatically converted
into literal format.