Community admin can now add both a desktop & a mobile logo.

- Client can upload a horizontal logo file
- Horizontal logo is shown in desktop mode
- Client can upload a square icon logo file
- Square logo is shown in mobile mode
- New correct sized square logo should be made from old logos
- For free tribes "Sharetribe" logo is shown as horizontal and "S" logo is shown as square.
- Global header navi items should have correct padding in all different states (logged in & not logged in, mobile & desktop)