Changed host of game logos

Newer game logos can't be found on cdn*.steampowered.com
Actual async requests for add_steamreview_userscore

Rewrote the add_steamreview_userscore function for actual async request.
It's much faster now.
Also if no reviews are available, the function will not request
anything.
Merge pull request #501 from Eisenzange/dev

Changed host of game logos