Require C++14 and CMake 3.1

See merge request walberla/walberla!79

- Avoid that defining points are aligned on a Plane
- Improve numerical stability of cross product

- cellIntervalToSlice more flexible

fix MPIEXEC_PREFLAG

See merge request walberla/walberla!80

Also remove some unneeded boost includes

Resolve "body filter to exclude bodies from PeVTKMeshWriter"

Closes #47

See merge request !77

Resolve "Rename setMass function"

Closes #46

See merge request !75

Dynamic refinement for pe module

See merge request !52

Reworked Body Mapping

See merge request !76

static calcMass and calcInertia functions are now available for all geometries

[API]: changed body mapping functions: removed most of them, added mapping-decider function, accomodated changes to test cases, added new mapping test case

CMAKE_FIND_ROOT to be able to find external libraries like openmesh
CMAKE_INSTALL_PREFIX for a possible later "make install"

Updated conda packages to cond build > 3.1.4 using host section
See https://conda.io/docs/user-guide/tasks/build-packages/define-metadata.html#host

Resolve "Add builds for GCC 7"

Closes #24

See merge request !37

- fixed problem with new conda by using new compiler mechanism
- added test file that is checked before upload
- open mesh recipe fixed
- force downgrade for conda-build, new tested version(3.2.1) of conda-build leads to an empty
  package and then failing test.. perhaps it is fixed with newer conda-build versions?

Enable dynamic refinement for coupled LBM-PE simulations

See merge request !73