Rename LinearReaction and PadeApproximant classes.
Linear reactions and PadeApproximant cleanup.

- rename class members
- reaction matrix - replace 2d array with vectors
- clean up code
Cleanup PadeApproximant.

- remove dead code
- unify the methods with LinearReaction
- unify reaction matrix multiplication
Reactions cleanup, include cleanup.
Reuse output vector scatter in DualPorosity and SorptionBase.
DualPorosity computation scheme switching.
Clean and rename variables in DualPorosity-compute_reaction.
Introduce record scheme_tolerance in DualPorosity.
Reference manual - describe DualPorosity scheme tolerance condition.
Make macros to handle returned error code.

- make macros to handle MPI, PETSc and ASSERT error code
- add unit test
Add inline function what check error.
Fix conversion between string and wstring in python loader caused by differences between python 2 and 3.
Merge with 1.8.0_master.
Fix publish step.
Copy Python include dir.

- Python 3.x needs also header files to work
Do not delete external_packages for release builds.
Deal with MPIEXEC .exe suffix under CYGWIN.
Copy Python include dir.

- Python 3.x needs also header files to work
Create output directory if doesn't exist.

- move code to main.cc source file (used only for Flow123D not for unit
tests)
Remove system/skip_to function.