Improve MapGraphics.java documentation

[cerus]

Feature description

The MapGraphics class is probably the most important class of this whole project. Thus it is very important to properly document everything. Some methods are not well documented (the description of drawText for example is literally just "Draws text") and need to be improved.

Relevant issues

No response

[cerus]

Comment if you want to work on this. If you have any questions or need some help feel free to contact me. Basic knowledge of Java is required.