Added javadoc to the ModLoader interface.
Added javadoc to the Mod interface.
Added getAvailableMods() implementation to the DirectoryModLoader.
Added updated javadoc to the getAvailableMods() method in the DirectoryModLoader.
Added loadExternal method to ModCollection for loading external mods
Made a method in Retrievers work with the SecurityManager
Merge branch 'issue112-available-mods' of github.com:Cardshifter/Cardshifter into mod-loading
Server now loads all available mods
Checking if directory exists before trying to load mods, to avoid crash
Merge branch 'client-server' into mod-loading
Fixed some Access doPrivileged issues when loading mods
Fixed bug for AI freezing if AI goes first, for games with no deckconfig
Using log4j in `GameClientLobby`
Fixed bug with my cards showing in opponent hand