Add documentation for the rest api

See merge request jonasblatt/ma-jonasblatt-dmn-verifier!5

A parsing error of the dmn xml has the same BAD_REQUEST response.

# Conflicts:
#	dmnverifierapi/src/main/java/de/unikoblenz/fgbks/core/dmn/verification/verifier/AbstractVerifier.java

see https://quarkus.io/blog/quarkus-0-23-2-released/

Merge branches 'develop' and 'feature-documentation' of https://gitlab.uni-koblenz.de/jonasblatt/ma-jonasblatt-dmn-verifier into develop

# Conflicts:
#	dmnverifierapi/src/main/java/de/unikoblenz/fgbks/core/dmn/verification/result/VerificationResultEntry.java
#	dmnverifierapi/src/main/java/de/unikoblenz/fgbks/core/dmn/verification/result/VerificationResultEntryFactory.java

Add map with all vdmn elements and their ids + Add better navigation through the vdmn object structure.