remove instance variables from BoardPanel

BoardPanel no longer keeps a width and height variable. Instead sets the
preferred width and height of the panel and uses that to set the gaps
and padding.
update BoardPanel boardChanged Javadoc
update ConnectNPanel boardChanged Javadoc
replace PlayerSelectPanel

Created PlayerSelectControl to replace PlayerSelectPanel. Uses FXML to
define the layout.
replace ConnectNPanel

Create ConnectNControl to replace ConnectNPanel. Uses FXML to define the
layout.

Update BoardPanel to work with ConnectNControl. Update Main to use
ConnectNControl