fix warning
fix cover
more informative error message
set application icon for gui
show available modules from python
replace GendatTest by pipeline description
create modules instead of executables
Vistle hub

Vistle hub is responsible for
- spawning modules (e.g. with mpirun)
- spawning UI
- interpreting initial python scripts

Vistle hub replaces the controller as the program started as 'vistle'.
This change is motivated by the difficulties of using MPI_Comm_spawn_multiple
for starting modules and controlling their placement onto nodes in a portable way.
DEBUG message was not used