move junit dependency to parent Maven module
update client and server constructors

Update constructors to check for null values where appropriate and
invalid ports. Add tests for these updated constructors.
fix client rematch code

It was previously possible for anyone with access to a Client to send
YES or NO messages to the server arbitrarily by calling
confirm/denyRematch at any time. Now the message will only be sent if
the client is waiting.
make methods private
update server output messages
add Javadocs

Added Javadocs and update a few parameters and variable names.
update ClientManager and NetworkGameManager

ClientManager now keeps track of each players last matchup. It will not
matchup two player who just played each other.

ClientManager and NetworkGameManager print a message when a player
disconnects.
update pom files

Removed redundant information (e.g. properties in child modules
inherited from parent pom). Added comments to pom files.

Packager module now depends on other the other modules to ensure that
they are built before copying files.

Client module copies class files from the core module so that they are
included in the JavaFX jar.

Server module creates two jar files. One with and one without
dependencies.
update README.md
update ClientManager

Check for null argument in addPlayer method and add test.