Start of the stix export tool
Python scripts to handle the conversion from a MISP JSON event to stix/cybox
First version of the STIX export implementation

- currently to_xml() has performance issues, if it's not resolved fast, it would be a good idea to move the export to the background workers

- some UI changes
removed old junk version of the export
Download stix xml / json result
Some cleanup
Merge branch 'feature/stix_export' into develop
Merge branch 'develop' of https://github.com/MISP/MISP into develop