Misc UI changes

[kra-mo]

Really nice app! Just made some smaller contributions to make the app feel a little nicer.

• Added more padding.
• Realigned some items.
• Added links in the about window.
• Made some misc string changes.
• Changed the labels using the title-3 style class to use title-4. It's good to have a higher amount of separation between styles next to each other.
• Less bland description.
• Removed the width-request of the button on the start page. It's bad for internalization.
• Made the header bar conditionally flat (until libadwiata 1.4 comes out anyway).

Looks like this is going to require some manual resolution because of the translation commit and my dumbass working on main instead of creating a branch :p

If you want any help with translations or anything else, you can reach out btw!

[kra-mo]

Alright, I've dealt with the merge conflicts