Hook up WMCores event aware lumi splitting.

Creates jobs by consuming lumis from the dataset until a user specified
number of events is reached.  This gives more evenly sized jobs for
datasets with more variation in lumi size.

Fixes #4199.  Additional changes not needed.  The database connection in
WMCore is optional, and if not present, the lumi size is estimated from the
number of events in a file.
Add a parameter to limit the number of jobs in the TW. Fix #4506
Move sleep in ASO transfers monitoring loop to beginning of loop; add a call to get_transfer_statuses before starting the loop; increase sleep time from 200 to 300 secs. Enclose all document retrieval from couch in try/except.
Merge pull request #4608 from AndresTanasijczuk/couchview

Improve situation with ASO view results in PostJob
Merge pull request #4603 from matz-e/better_splitting

Hook up WMCores event aware lumi splitting.