admin: replace "give admin" button with permissions widget

[stoneage-mta]

I will send another PR to do the same/similar to admin2 in near future.

[xLive]

I've an idea for the design, something like this:

What do you think?

[stoneage-mta]

Looks good and I can apply something similar, but first lets wait for other opinions.

[Allerek]

I've an idea for the design, something like this:

What do you think?

Thats cool, simple and easy to understand, even newbies will understand that design.

[Dutchman101]

I've an idea for the design, something like this:

What do you think?

I like this design more than the current one in PR, just add something on the left side to clarify those are the available groups (to assign) and something on the right to clarify those are the current groups for that user

[stoneage-mta]

bruhhh looks like i just ruined my branch

[stoneage-mta]

I think I finally managed to fix it. Sorry for the useless commits, let me know if you think is better to create a new PR, I still learning this thing called git.

Anyways, this is the new design:

Please comment below if you have any suggestions.