Channel up and down for webostv

[stephanerosi]

This enable using the next and previous buttons on the media player interface to switch channels up and down, which is the desired default behaviour for a television.

Checklist:

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

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

• [] Documentation added/updated in home-assistant.github.io

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

• [] New dependencies have been added to the REQUIREMENTS variable ([example][ex-requir]).
• [] New dependencies are only imported inside functions that use them ([example][ex-import]).
• [] New dependencies have been added to requirements_all.txt by running script/gen_requirements_all.py.
• [] New files were added to .coveragerc.

If the code does not interact with devices:

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

[homeassistant]

Hi @stephanerosi,

It seems you haven't yet signed a CLA. Please do so here.

Once you do that we will be able to review and accept this pull request.

Thanks!

[syssi]

It's a breaking change somehow but I support the suggestion!

[ghost]

When this PR will be implement to master Home Assistant ?

[ferdydek]

Could you please make sure this works only when "Live TV" is the active source.

Mostly these buttons are for next/previous track/menu, and since most people use services like plex netflix youtube etc rather than live tv, the intuitive default behavior would rather be previous and next (episode, video on playlist, etc) and not tv channel manipulation.

[stephanerosi]

@ferdydek
You're right, I'll update the pull request

[stephanerosi]

@pvizeli
I updated my branch. How do I update my pull request? Should I create a new pull request?
Thanks