first implementation of random stepping field
extend obstacle_generator plugin

The plugin now allows to create random stepping fields made from
capsules or boxes with arbitrary inclination angles. Obstacles
can even be rotated to match said angle.
add ranged random number generators to mathUtils

Two random number generator functions were created, one for providing
uniform random numbers in a given range and one for normal random
numbers also cut off at a given minimum and maximum. For the normal
random numbers, the Box-Muller-Transform was used.
remove random num generator from obstacle_plugin

The functions were moved to mathUtils.
specify random num precision in obstacle_generator
correct box height and z pos in obstacle_generator

This allows boxes to be created only as large as needed, in contrast
to capsules which have to be twice as large larger as we only use
half of them. This means boxes have to be moved a bit further down on
an inclination such that not their middles, but their fronts
are in the correct height with respect to the inclination surface.

We still have to take another look at inclined obstacles, though.
obstacle_generator: added documentation
obstacle_generator: added documentation
obstacle_generator: changed default values
obstacle_generator: calculate obstacle number for grid mode
obstacle_generator: simplify geometry calculation

A number of geometrical problems resulted from setting the boxes to
their actual height. It turns out that setting them at twice their
designated height and thus treat them like the capsules, where
only "half" of the geometry is used, simplifies a lot of things.
This is a results from the rotation always occuring at ground level,
which is where the origin of the obstacles is if they are twice
their specified height.