Merge pull request #22 from cmhbenjamin/master

Sending/ receiving, message spliting working.
Merge pull request #23 from cmhbenjamin/master

small changes
Merge pull request #24 from cmhbenjamin/master

implemented file transfer
Implemented commands /help, /users, /exit. Cleaned up code. Implemented
user tracking. Each message is led by the sender's name. This is then
used to keep track of list.
Minor bug fix. Now users who are already on the network don't get
re-added. Doesn't allow for duplicate usernames.
Update ConsoleUI.java
Update MulticastClient.java
Update ConsoleUI.java

File sending problem fixed
Update FileProcessor.java

Fixed file problem
handle errors in user management