DDNet Tab / Server list

Notes:
- Server list in json format: https://eastbit.net/priv/serverlist.json
- Transfer zlib compressed
- Server list request is initiated on client start and on DDNet server list refresh
- br_filter_exclude_countries contains a comma seperated list of excluded countries, elements which aren't defined in the serverlist received by versionsrv are removed automatically so the exlusion list doesn't contain dead elements
- The DDNet tab still bugs the interface in 5:4 resolution
- DDNet tab is not part of ingame serverbrowser yet