Add LCN scene platform

[alengwenus]

Description:

This adds the LCN scene platform. The implementation allows the activation of LCN scenes which have been properly programmed into the hardware modules.

Pull request with documentation for home-assistant.io (if applicable): home-assistant/home-assistant.io#9545

Example entry for configuration.yaml (if applicable):

lcn:
  connections:
    - name: myhome
      host: 192.168.2.41
      port: 4114
      username: !secret lcn_username
      password: !secret lcn_password

  scenes:
    - name: Romantic
      address: s0.m7
      register: 0
      scene: 0
      outputs: [output1, output2, relay1, relay3, relay5, relay8]
      transition: 5

Checklist:

• The code change is tested and works locally.
• Local tests pass with tox. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the development checklist

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in home-assistant.io

If the code communicates with devices, web services, or third-party tools:

• The manifest file has all fields filled out correctly. Update and include derived files by running python3 -m script.hassfest.
• New or updated dependencies have been added to requirements_all.txt by running python3 -m script.gen_requirements_all.
• Untested files have been added to .coveragerc.