merge relevant existing forks

[tillmo]

merge all relevant existing forks. This is a prerequisite for #2094, because #2094 will make merging much harder (part of the #2094 work has to be redone in the forks as part of a merging process, which is cumbersome).

[tillmo]

Potential forks, pull requests and branches to consider:

• Marie Farrell's logic EVT #2149 PhD thesis Marie Farrell
• https://github.com/spechub/Hets/tree/1899_gdol_parser Mihai's work on GDOL @mcodescu please have a look if you can merge master into this branch
• https://github.com/spechub/Hets/tree/morphism-search PhD thesis Immanuel Normann
• draft UML logic #2150 Martin's work on UML
• https://github.com/spechub/Hets/tree/1693-datatypes-for-DOL some unfinished work on supporting more of DOL
• Fix reading long request bodies. #2151 One small commit remaining from Eugen Kusksa's masters thesis
• Rigid casl #1845 Mihai's work on Hybrid logics
• https://github.com/spechub/Hets/tree/1402_hol_light_package
• https://github.com/spechub/Hets/tree/improve_rdf
• https://github.com/spechub/Hets/tree/1325-exluding-clause @mcodescu please have a look if you can merge master into this branch