Added multivisor protocol with 'service' hardware

Closes #18 (closed)

This PR provides a support for Multivisor protocol.

I would like at some point to be able to describe Multivisor services for some detectors, like Lima detectors. This PR is a step into that direction.

• Added a service abstract hardware description
• Added a multivisor protocol based on http client
• Added a Multivisor service hardware
• Notice that i have copy-pasted a part of the code under GPL for the Multivisor client. I could ask for a change of the license.

The protocol have to be defined in the hardware.yml such way

protocols:
  - id:  multivisor
    type: multivisor
    address: http://localhost:22000

Then, new services can be described using the UID used by Multivisor

  - url: multivisor://mainstation:id00:metadata

Finally the hardware can be displayed in the layout

    - type: form
      contents:
        - type: component
          title: Metadata
          component: hardware
          id: mainstation:id00:metadata