19069: Workflow launching improvements.

19069: Workflow launching improvements.

* Hide the broken, mostly redundant workflow panel from the left tree
(can still launch workflows from "+NEW -> Run a process")

* Hide unsupported "presets" element

* Don't require #main to be a workflow

* Change "workflowUuid" property to "template_uuid" property for
consistency with existing usage in workbench 1 and arvados-cwl-runner

* Give process a default name

* Assign default output collection name "Output of {name}"

Arvados-DCO-1.1-Signed-off-by: Peter Amstutz <peter.amstutz@curii.com>