Add PipelineRun in the tree as a root node

[siamaksade]

PipelineRuns can be standalone without referencing a pipeline and should be displayed in their own folder, in addition to under a particular pipeline

[gorkem]

There can be too many PipelineRuns without a way to group them together that folder can get very crowded. Should we have a folder for orphan PipelineRuns only?

[siamaksade]

@gorkem PipelineRun and TaskRun can embed the pipeline and task using pipelineSpec and taskSpec. Those won't show up anywhere.

Limiting the number of items (#127) should apply here as well to address the too many items problem.