Rest refactor

add badge with link to maven central

Solution: switch to left outer join to get all results + add variable name non-null to filter out all 'wrong' results due to the outer join

Reverted manually commit https://github.com/Activiti/Activiti/commit/1fd11705d65efd6f47382c0f0e356189f4c8563b : restoring original job executor as we're implementing the new, improved one (see previous commit)

Introducing the next generation of the job executor. Faster by great margin. Still very experimental and untested.

Still a lot todos:
- Cleanup failed jobs thread
- Exclusive jobs are not handled
- Suspend is ignored
- Unit tests
- Docs

Fix as per https://github.com/Activiti/Activiti/commit/90fa5e5768974df08162904274546535c6559fef#commitcomment-7975412

restored the activiti + spring boot unit tests.

Spring Boot integration

log reports configuration method incorrectly.

Userpic

REST Delete ProcessInstance IdentityLink

Activiti 5.16.4 userguide ch07b update

Update from original