cleaned up game() and fixed some bugs.

made a method
bool grid.move(char);
that checks if the input is valid and calls void fill(int).
also there was an ugly bug (it used Grid.Max instead of grid.localMax -
so 7,8,9 were impossible to enter in challenge mode and loaded games)

tried to make Game() easier to understand (put some of the things it
did in other functions etc).
fixed bug with

if game was won with last remaining move in challenge mode it counted as
a loss.
minor stuff

removed some unnecessary Prints/Clears.
tell user if settings were invalid and fixed.
the start cell is now white and has a zero in it.

easier to start as it was almost impossible to find the middle in bigger
games earlier.
Merge pull request #6 from oerpli/master

cleaned up game() and fixed some bugs.