Simplified login pages follow-up: Style Register and Reset Password links

[quicksketch]

Description of the need

Every time I've shown the new simplified login links, I've had to explain that it "looks better" when there are two links, or describe a single link is in an <ul> tag. We should style these links so they look good even if there's only a single one.

Current screenshot:

Proposed solution

Hide the default bullets and center the link items in Seven only. Leave contrib themes to imitate or style as desired, since this is opinionated:

One link:

Two links:

Hypothetical wrapped links:
(I couldn't think of a way to style this without resulting in a trailing/leading dot)

[olafgrabienski]

Yay, this looks so much better than the default list style. I've had a look at the sandbox, works for me, also on the other login pages (user/register and user/password).

[argiepiano]

Personally I don't mind the bullets. I find this centered list a bit strange, but that may be just me.

On the other hand, since this change is only happening for Seven, this will be lost when choosing a different backend theme, or choosing the front end theme for the simplilfied login.. And we have to be careful about making it global, as it will affect the bullets in the "links" appearance too, which will look pretty strange given that we are using the front end theme for the "links" appearance".

[docwilmot]

I actually prefer the bullets, also find the centering a bit strange. Maybe nicer bullets?

[indigoxela]

I left some comments on the PR. Suggestions for consideration mostly. 😉

Personally, I'm also fine with the current ul display, but also see the visual improvement. Not sure about the centering, but I'm fine with it, too.

[avpaderno]

I like how the links are rendered, but I also do not dislike the links rendered as bullet list.

I would like more the new style if also other themes could use it.