quantity.Discrete/zeros will return an empty array if the requested size for zeros contains 0 as size. quantity.Discrete/compose works on quantities defined on quantity.EquidistantDomain

- misc.unique4cells: new function similar to unique, but works for arbitary cells
- misc.getMinimalInternalModel: new function to calculate minimal internal model as state space

- ode45 seems to be more precise for this kind of problems then ode15s
- successive approximation
- faster implementation for the case that the integral term can be neglected

misc.solveVolterraIntegroDifferentialIVP: new script to solve a system of volterra integro differential initial value problems

quantity.Discrete & Symbolic: bugfixes because of string inputs in plot + Symbolic.subs + Symbolic.gridName2variable

Change the parameter order of quantity.*/diff
Now, the domain name wrt which the derivative should be taken is the second argument and the order of the derivative is the third.

speed up of the unittest utilizing setupOnce