Continuous Integration and GUI for CartMeshes

New features:

• Improved CMake support, require at least CMake 3.0
• Added continuous integration support via Gitlab CI
• Added GUI tool as a frontend for HOPRs internal CartMesh grid generator, to build simple cartasian meshes.
• Add some more documentation

Removed features:

• Custom makefile support has been dropped in favour of CMake

Deprecated features:

• Converter from old to new mesh format will be removed in the next release of HOPR

Now support for non-conforming meshes and CMake

New features:

• HOPR now supports non-conforming meshes with a ratio of 2->1 per direction
• CMake has been added as a build system
• Improvements in the Gmsh readin routines
• Code refactoring to be nearer to the Flexi-style
• General bugfixes and performance improvements

HOPR is now hosted on Github!

New features:

• HOPR is now hosted on Github! All new releases can be obtained here in future.
• Documentation and build structure for Github.

Fixes:

• Fix readin of CGNS boundary conditions of types ElementRange and ElementList.