Fixed Test and address #1 partially

BoardTest's properties test is split up into smaller tests now to make it easier to track when stuff breaks.
Also I tested the rows wrong, so that was fixed.
Calculating the rows of course is fixed as well.

I also added the ability to get the Entry based on its x,y values and of course a get Value with x,y.
Added Documentation, Protection changed

I added Documentation in the code to be parsed with JavaDoc.
Also I changed the write method and the corresponding test to mirror a change I wanted to make. Entries should only be write protected when they are part of the original puzzle. Protecting "custom" values doesn't make sense if we have to guess the right entry later on.
Merge remote-tracking branch 'origin/board_logic', Concludes #1

The Board is done, next up: Solving