Image url getters for HelixChannelSearchResult, HelixGame and HelixVideo

[CaveMobster]

Feature Request

Hi again 😄

I noticed that HelixChannelSearchResult, HelixGame and HelixVideo don't have an image url getter like HelixStream does for the thumbnail url, but I think they're really useful. Shall I implement them?

[d-fischer]

The channel search returns non-templated profile picture URLs. For the rest, sure, you can go on and implement helper methods.

[CaveMobster]

My bad, the Twitch documentation says it returns variable dimensions, but it looks like the documentation is incorrect.

I'll get the others done, thanks!