Include more options to initializate stetes

Description

Right now it is only possible to initialization of states by using analytic functions. Of course this is not sufficient since there might be data available to set the initial conditions of the biological spices. It is therefore needed other means to allow external data to enter the program.

Proposal

There are several options that we can explore:

1. Use the gmsh format to attach data to the initial grid. In this case we would have to develop the node/element data parser in dune-grid. In this case the idea would be to attach data to every vertex and use a P_1 polynomial to interpolate data
2. Use an standardized image format and interpolate it into initial coefficient vector. In this case TIFF seems to be the most interesting one since it can have different types of compression and can hold extra information about spatial distribution of its data.
3. Assuming dune-copasi will work as a library, one can use a input of a function which can be evaluated in space and that can be internally interpolated.

How to test the implementation?

It depends on the chosen option.

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