This unifies the code color-scheme code and makes
adding new schemes a little easier.

This refactors the `user_color_scheme_class` to use
a hash with a default.  This prevents problems
with workers that don't have access to the
current_user.

Fixes issue #2758

Also specify separate project factory for project with filled repo

Since search_autocomplete_source rendered with raw all human input should be sanitized to prevent XSS

Fixes #2617

* remove unused method
* simplify gravatar_icon

always use proper size value
do not show alt text when avatar image not loaded