make Point2D immutable

A first step towards more thread safety. Point2D coordinates can now not be modified separately, which removes the possibility of temporary inconsistencies.
make lazy initialization of singleton synchronized
unbox primitive types

There is no need to use boxing if the fields are not supposed to be synchronized upon. When passing around primitives, they actually are copied and no extra encapsulation is needed.
make constants final
convert CRLF to LF line endings
make Eye immutable
make GazeData immutable

Boxing of primitive types bears some risk (escaping references etc.). This has been removed. Moreover, GazeData can now be instantiated by hand for testing purposes (which will be added later).