chore(rest): update docs according to new exception handling

contributes to CAM-733, CAM-694
Merge branch 'live'
feat(rest): add DELETE process instance docs

contributes to CAM-641
chore(cockpit plugin tutorial): Fixed some typos
fix(link): fix link to javadocs from api-references site
Merge branch 'master' of https://github.com/camunda/docs.camunda.org
feat(rest): add docs for PATCH process instance variables

closes CAM-747
Merge branch 'master' of github.com:camunda/docs.camunda.org
feat(rest): add doc for GET, PUT, DELETE single instance variable

contributes to CAM-642
fix(rest): remove response media type for put and delete
fix(rest): fix introduction links in method descriptions

closes CAM-751
feat(rest): add docs for execution query and count

contributes to CAM-637
feat(rest): add docs for GET single execution

contributes to CAM-638
feat(rest): add docs for signalling executions

contributes to CAM-638
feat(doc): propose simpler rar name
docs(cockpit-plugin): update how-to to latest version
feat(was): add docs for all webapps on was

related to CAM-441
Merge branch 'master' of github.com:camunda/docs.camunda.org
chore(rest): change modify variables docs from PATCH to POST

contributes to CAM-642
Merge branch 'master' of github.com:camunda/docs.camunda.org