HPCC-8861 Refactor LogicalFiles

To match ESPWorkunits:
Make ESPLogicalFile a singleton.
Make DFUWUQueryWidget + LFDetailsWidget a MVC
Implement missing actions.

Signed-off-by: Gordon Smith <gordon.smith@lexisnexis.com>
Merge pull request #4054 from GordonSmith/HPCC-8861

HPCC-8861 Refactor LogicalFiles

Reviewed-By: Kevin Wang <kevin.wang@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>