Steam integration update

Improvements: - Added Steam Rich Presence - Friends are now able to join to the server you are playing on directly from the friends list - Your friends list entry now additionally shows your status in the game - Servers now show up in Steam's server browser and are joinable from there

Fixes: - The active player number is now shown correctly both in the in-game and Steam server browser - Pressing controller buttons on the photosensitivity warning and logo animation now skips the warning or logo again - As a result, pressing controller buttons during the warning and logo no longer controls the menu behind