Revert "remove logo that wasn't being used"

This reverts commit 8ccf219ac8d27bd2222d6caef04bd61702e2fe3c.
add favourite_colour to seeds.rb
use the favourite_colour as the user highlights rather than the first letter of their username
make signup used custom-colour directive instead of inline style (issue with IE i think)
update colours to more gelati style - just playing with things