Fixes grammatical consistency and small changes

This commit adds consistency to small things like periods, commas,
and gives additional information to buttons and headers, etc.

Fixes #2002, #2005, #2003.

See merge request !1570

Tests expected specific string capitalization for headers.

This reverts commit 7d5f86f6cbd187e75a6ba164ad6bfd036977dd07.

This commit moves the note folder from
/public/uploads/note
to
/uploads/note
and changes the uploader accordingly.
Now it's no longer possible to avoid the access control by modifing the url.
The Avatar upload has been refactored to use an own uploader as well
to cleanly seperate the two upload types.

We were having the following issues:
- the indicator would sometimes stay red even if the password that was
  entered was long enough;
- the indicator had a middle yellow signal: what does that mean?
- the red/green backgrounds were not color-blind-friendly.