22141: Refactoring to reduce circular import dependencies

22141: Refactoring to reduce circular import dependencies

The DataExplorer test started failing with the error "can't access
lexical declaration 'DataExplorer' before initialization".

I couldn't figure out exactly what I did that caused this to suddenly
start being a problem, but running the 'dpdm' tool on the codebase
showed a huge number of circular imports.

I moved several symbols directly or indirectly involving DataExplorer
out of the 'view' modules over to the 'action' modules and fixed
everything to import from the new location, and the DataExplorer test
is passing again.

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