User menu & theme switcher update on all resolutions

[diksipav]

Update user menu on desktop and mobile.
Update theme switcher on mobile.
Move secret-keys page to the top level /secret-keys.

[jaclarke]

• Menu items are missing the border-radius
• Scrollbars (probably not a big issue as mobile doesn't usually have scrollbars)
• When opening the theme switcher dropdown, the tooltip is visible on the right for a second
• Theme select seems to be slightly taller than the menu items

Hey, I already fixed these things in a new commit. Will just double check the tooltips, i saw them but after screen refresh didnt see them anymore (without changes, and this only in firefox).

[jaclarke]

Was this commit meant to be in nebula-ui? Ignore this, I see the other part in the nebula-ui PR.