Copied functionality from minimum refinement function plugin.
Added entry to changelog.
Added tests for the maximum refinement function.
Added output from maximum refinement tests.
Additinal parameters for spherical shell initial conditions and geometry

Updated geometry_model/spherical_shell.cc
Can specify number of mesh cells created in the first time step.

New parameter:
  int Cell count

----------------------
Updated initial_conditions/spherical_shell.cc
Can specify the number of convective cells and their orientation.

New parameters:
  int Lemniscate number
  double Rotation offset
Replay Joey Durkin's second set of changes.

Something had gone wrong with these patches and they ended up deleting and re-creating a lot of files. This commit simply applies all functional changes that were part of the commit gone wrong.
Update a few pieces of the documentation.
Reunite a function with its documentation.
Reindent.
Be more verbose in a warning message.

In order to track down what's happening, knowing which file we were trying to write to turned out to be about as useful as knowing the processor number.
Minor edits to some text.
Merge pull request #172 from bangerth/doc-fixes

Minor edits to some text.
Create a postprocessor for complete material output.
Merge pull request #168 from bangerth/more-verbose-error

Be more verbose in a warning message.

In order to track down what's happening, knowing which file we were trying to write to turned out to be about as useful as knowing the processor number.
Address Timo's review comments.
Document the parameter better.
Add a test to verify that we can create meshes with different numbers of cells in the perimeter.
Better documentation.
fix diffusion creep for n!=1
Address a number of issues brought up in review.

Specifically:
- Add changelog entries.
- Add a test for the hexagonal initial temperature model.
- Unconfuse myself by moving functions belonging to the same class closeby.
- Minor cleanup.
- Fix descriptions of tests at the top.
- Add a test for the octagonal perturbation.
- Add another test.