Toolkit2: Allow users to share binaries, move them accross computers, etc.

The new ExaHyPE Parser C++ infrastructure currently does a suprocess to call the Toolkit in order to convert old-fashioned specification files. To do so, the call to Toolkit/toolkit.sh is hardcoded, including the path.

This raises problems in certain use cases:

• The user shares his Executable to another user on the system/cluster but does not make the access permissions correctly for the Toolkit
• The user copies only the Executable to another machine but not the overall Code (especially not the Toolkit code)
• The user renames the path to his installation (probably when cleaning up his home directory) but wants to keep an ExaHyPE build working (obviously this is not possible)

We have no solution for all these use cases, but we should include checks in the C++ code to deal with them:

• Check whether Path/to/Toolkit/toolkit.sh exists, is readable and executable