Do only catch TimeoutExceptions in MasterServer::getServers()

This prevents errors from being silently discarded.
Fix visibility of GameInventory::getAppId()
Fix some comments
Let S2A_RULES and S2A_PLAYER packets throw PacketFormatException
Fix getInventory() of Portal2Stats and TF2Stats
Fix return type of SteamPacket::getData()
Make RCON termination conditional

Only non-empty RCON replies will be accompanied by a termination
request. This will prevent timeouts during `changelevel` and similar
commands.

See koraktor/steam-condenser#221
Fix SourceServer tests
Simplify GameStats::_getBaseUrl()
Version bump to 1.3.6
Merge branch '1.3-stable'