board-builds itself

Now the entire board is build by calling "new Field(this);" from Board
:) Field is made in a way that it can self-build itself. It only needs
the boardDimension and then creates all the fields, links all with each
other (a non-border field has 8 neighbours that are linked for direct
access in winCheck) and fills the 2D array in Board on the go. Very
happy with that architecture :) [#1]
Islands need more improvement though,