Add an interface for an yet to create heating_model in simulator.
Add a heating_model pointer to simulator that gets initialized. Compiles well but no run tests so far.
Add the declare parameters function for heating model interface. Use heating model->radiogenic_heating_rate in assembly.
Add the old radiogenic heating functionality in a new heating model constant heating.
Add a test and a future cookbook for radiogenic heating.
Add a function heating model. set_current_time now gets called at the beginning of a new timestep.
Add a future cookbook for space- and time-dependent radiogenic heating.
Remove parameter Radiogenic heating rate from tests.
Remove parameter Radiogenic heating rate from cookbooks.
Remove parameter Radiogenic heating rate from benchmarks.
Improve description in constant heating plugin.
Removed the parameter Radiogenic heating rate from parameters.cc. Now it is only available in the 'constant heating' heating model.
Change manual to reflect changes for radiogenic heating.
Improved documentation of heating models. Also moved the set_current_time function to a generic update function in the interface and all existing plugins to be similar to material model and gravity model.
add a new material model and cookbook with reactions between compositional fields
Changes in manual regarding compressibility and Juliane's fixes to certain terms
fix up manual after 1baf0382dc80
temporarily fix convection-box.prm until we figure out what happens with the linear solver.
Merge pull request #1 from jdannberg/composition-reaction

add a new material model and cookbook with reactions between composition...
Add figures.