Changed implementation of integration for "Discretes". The input arguments are now consitent with the matlab "int" function.

*) Allow to set empty quantity.Discrete objects with certain size
*) added the isConstant property for the quantity.Discrete
*) Implemented a cast to the quantity.Operator object
*) Implemented a cast of empty quantity.Discretes to quantity.Symbolics
*) Fixed bug in "on()" for constant quantities
*) Fixed some functions to work with empty quantities
*) Added a settings object to use global settings
*) plot function returns now an array of the figure handles
*) Re-implementation of the quantity.Operator object

Discrete.plus(): somehow I found a combination, for which plus didn't work... fixed it and created unittests

Added the ability to concatenate quantity.Discrete objects with numerical values. In this case, for the numerical value a quantity.Discrete object is initialized.

in my eyes the concatenation of arrays should not change properties of the objects and should also not create new instances. This has to be done before the concatenation or in a special version.

- bugfix in get.grid()
- horzcat, vertcat, cat now ensure, that grid and gridName of all quantities to be concatenated are compatible, by changing the grid to the finest grid.

Initial checkin of the matlab library for the control and faultdiagnosis of infinite dimensional systems