Store parameters like variables in result storage object

[Eike]

Currently parameters are stored separately in the simulation object. This is useful for manipulating the simulation from Python, but for later data analysis parameters are inaccessible. Especially parameters are not stored on disk.

 - Therefore parameters should be stored in the results storage object too.
- Therefore parameters should be stored in the results storage object too.
 - Parameters should be accessed through the same methods like variables.
- Parameters should be accessed through the same methods like variables.
 - Parameters should be returned so, that they can be easily graphed along variables.
- Parameters should be returned so, that they can be easily graphed along variables.

See bug: #28
https://sourceforge.net/apps/trac/freeode/ticket/30