Place menubar at the bottom on mobile

[juliusknorr]

This was raised by @jancborchardt as a quick enhancement for making the menu bar easier to access. We could move it to the bottom of the screen on mobile devices. Similar to other notes apps, iOS Notes. This came up when reviewing assistant usage on mobile

WDYT @max-nextcloud @marcoambrosini

[marcoambrosini]

I think it's a good idea