Change icons and title when build on RTD from a PR

[parulin]

By checking some environment variable from Read The Docs in conf.py, we can determine if the build is made from a PR build. In that case, the HTML title is slightly different and instead of normal icons, we use red-tinted ones.

That way, putting some links to the PR builds overview will be clearing distinct from the official build.

[maiska]

I am not sure that red coloring is the best way to approach this. It adds some uneasy feeling to the person viewing the docs.
I think it suffices that when a build is made from a PR - it is highly visible in the url, you cannot miss it :) and there is the option on the side, to show a diff :)

[parulin]

It adds some uneasy feeling to the person viewing the docs.

That was my goal here: if I put a link to a PR in the forums, I want the reader to feel like it's not official.

But if it's unpleasant for the maintainers, I can just touch the opengraph meta data?

[maiska]

My point is not being unpleasant for the maintainers but for the person to read this. Maintainers are in this context not relvant imho. opengraph sounds good? and perhaps not red? it is alarming somehow :) perhaps shade of blue that is mixed with gray as to indicate 'inactive' meaning not merged yet? :)

[parulin]

I choose red to mimic the "untrusted" qube. Very few people should be reading the PR builds and being alarmed in this context is better than too confident, don't you think?

I used qvm-get-tinted-image to make the pictures so if you want another color, just tell me the hexadecimal value I need to use :)

[maiska]

right now I think there are just two subjective approaches to the decoration of the message "This is a PR".
and perhaps it's best to let someone else decide :))

[parulin]

Okay so there are two solutions, and we would like another opinion:

1. the current PR
2. just changing the OpenGraph meta data and using another color to tint the images