Fixed #16: multiplication of symbolics is working again

misc.variables2tex : added handling of function handles that cannot be converted to symbolic. This happens when an interpolant is evaluated in the function.

Bugfix quantity.Function.on = quantity.Symbolic.on :  didnt work for quantities with more than 2 grids until now. Values were always concatenated along the second dimension so far. Then reshape resulted in wrong result.

quantity.Discrete: added comment that the median works over multiple dimensions only for MATLAB 2019a or newer.

misc.isequalF implement functions with multiple arguments by using quantities and include the case where nargin = -1. This is important for functions that result from a quantity that results in constants.

Finished new implementation for the case of equalDims in misc.multArray . Simply use old implementation if no equalDims are present. It is much more performant than new implementation in this case.

Started rewriting multArray.m. old implementation is faster if there are a lot of dimensions that need to be created by the pointwise multiplication. Needs some check to decide what to use or a combination of both

Bugfix misc.multArray. Corrected unittests.misc.testMultArray to account for the special, priviously buggy case where the dimension multiplied was the last dimension and the equal dimensions were more than one but not at the beginning.

Fixed bug, so that the gramian for the trajectory planning can be computed also for instable systems

Function to compute the transition for a state-space system from x0 to x1. The transition is computed on the basis of the gramian controllability matrix