User settings page

[cfaisy]

Separate general settings and user settings and add new page for user settings.
Add theme modification in user settings.
Remove top right button for theme/log out and move it in left menu, on avatar icon. (New sub-menu for log-out and access to user settings)

[mattLLVW]

for this kind of PR, could you please open an issue so we can discuss it first?

I don't really see the point:

• now the user settings menu is hidden.
• you have to look in 2 different places to manage settings.
• the button is not working properly.

On another note, please don't add semi-colons, it add noise to the PRs.