Improve link styling for high-contrast theme

[The-Compiler]

Looking at #84, the high-contrast theme originally was created for eReader
devices.

On my device (an Onyx Boox Nova Pro), it works quite well, but both links (being
a rather dark blue) and normal text get rendered as black, making it impossible
to tell them apart from normal text.

This change makes links black and re-adds the underlining.

cc @shtrom

[di72nn]

We currently have a high-contrast and an "e-ink" theme, which only differ in that the "e-ink" one has font-weight set.
I think it would be better to modify only the "e-ink" theme (since I have no idea what preferences other users of the high-contrast theme have), would it be ok with you?

If so, I would suggest to simply rename weighted-font style to something like e-ink (in CSS and here) and add your changes with that style.

Update: Now I can see you suggested renaming weighted-font yourself, I missed it.

[The-Compiler]

Yeah, I wasn't sure about it - not sure who would use the high contrast theme without an e-ink device. If we're thinking of e.g. people with bad vision, I guess it'd make sense to have the link text in black (to have a high contrast) as well.

Some related discussions:

• HTML link appear too bold and underlined #173, there @Strubbl said:

For high contrast themes in light and dark i would keep this bold and underlined, because color would decrease the contrast.

• Remove font-weight change for High Contrast theme #775 which introduced the separate e-ink theme, since people seem to use the high contrast theme on AMOLED screens - from @tcitworld:

Isn't the black theme also used on regular Android devices as an "energy saving" theme for AMOLED devices ?

Also pinging @tenkabuto @di72nn ^{(whoops, that's you!)} @silberzwiebel from there in case they have some more insights.

I personally don't care much either way - let me know how to proceed and I will 😉

[tcitworld]

I agree with suggestions from @di72nn. Let's at least make the weighted-font rename.

[silberzwiebel]

I'm using the e-ink theme right now on an inkbook prime and can tell apart links from text just fine. Links are light-grey, text is black.

[The-Compiler]

Hmm, okay, seems like this is only needed for Onyx devices then. After thinking about it some more, I'd propose this:

• Rename weighted-font to e-ink anyways (just because it makes things more clear)
• Try working around Onyx' stupid style injection (so that links are grey instead of black)
• If that's impossible, add a new "underline links" options to the settings, so this can be turned on independently from the theme and only for e-ink devices where this is needed.

How does that sound? Closing this in the meantime. I'll try to follow up with new PRs for these, but it might take a while, as I have quite a bit on my plate right now.