Merge branch 'cleanup-1' into 'master'

Remove various visualization support

This merge request removes various visalization support from UG. This includes export to several file formats such as AVS, DataExplorer, Tecplot and ParaView as well as removing the X11, COVISE and pV3 support. All of them are not needed for using UG as a grid in DUNE which already provides its own support for data visualization.

See merge request !9