HPCC-11051 Sporadic empty lists

An occasional dgrid exception was causing several "issues" within new ECL Watch,
most obvious was empty lists, but could also have caused forms to be empty or not
refreshed etc.
Improved loading message for slower list loads.
Improved default store population.

Fixes HPCC-11051

Signed-off-by: Gordon Smith <gordon.smith@lexisnexis.com>