Design/kelly nudges

Some design tweaks to add to the tweaks mhjb was doing

uploaded to new logo in header of logged in view
Changed from dark header to light header
New icons in the header 
Added simple subtle background pattern
Changed hover/highlight colour from light blue to light yellow (to match loomio brand)
Added google font 'Arimo' for headings
Made logged out header links orange (loomio orange)
Changed the blue of the default link blue