Handle calibration

[BECATRUE]

Feature you want to implement

Users often request WLM calibration, hence the server should support it.

How the feature is implemented

The workflow is as below.

1. A request to calibrate is received.
2. If there is a task handler, i.e., the measurement is running, it returns an error.
3. Otherwise, it creates a new task handler and sends the messages to 1) calibrate and 2) close the WLM connection.
4. Task handler receives the messages, and perform them.

The calibration info is stored in config model.

Additional context

Whenever it calibrates, the task handler is recreated and the WLM connection is reopened, thus it looks too inefficient.
I will improve the workflow in #36, so please ignore this for now.