Further cleanup frontend

[balloob]

Description:

Clean up frontend component after extensive cleanups on the frontend JS.

• Remove telldus image
• [Breaking Change] Remove ability to register panels directly with the frontend component. Register with custom panel component instead.
• No longer pass data to index.html template that is not being used
• @asyncio.coroutine -> async

Example entry for configuration.yaml (if applicable):

frontend:

Checklist:

• The code change is tested and works locally.
• Local tests pass with tox. Your PR cannot be merged unless tests pass

If the code does not interact with devices:

• Tests have been added to verify that the new code works.