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
feat(rest): add docs for execution variable methods

- GET, PUT, DELETE single variables
- GET, POST multiple variables

contributes to CAM-639
fix(WAS): adjust WAS installation guide - Installing camunda platform App
feat(rest): add docs for message event triggers

contributes to CAM-635
rem(wireminds): wireminds is only in camunda.com
Merge branch 'master' of github.com:camunda/docs.camunda.org
Merge branch 'master' of github.com:camunda/docs.camunda.org
Merge branch 'master' of github.com:camunda/docs.camunda.org
docs(was): add download location notice

related to CAM-441