Connection improvements

Added Assets class which stores filepaths to source files.
Added connecting icon - displays when client attempts to connect to a
server.
Added interuption icon - displays when client has detected a connection
problem with the server.
Added multiple packet sending during connection step to ensure server
and client both communicate.
Fixed player ID interchanging/overriding.
Fixed client not able to join a new server if previously joined a
server.
Refactored redundant code.