Move Dashbuilder documentation to KIE docs

A new entire book for dashbuilder is expected to be created within the KIE docs repo by just moving the current dashbuilder book from its current location:

https://github.com/droolsjbpm/dashboard-builder/tree/master/docs/quick-start-guide

... to the target KIE doc repo:

https://github.com/droolsjbpm/droolsjbpm-knowledge/tree/master/kie-docs