first go on co-existing Sync and Async download modes

to much benefit of Async yet
isReplicatable is unnecessary condition

Some objects are not "isReplicatable" (e.g. ContentVersion) but can still be queried and backed up
checking if file is blank in Bulk mode is different from Sync mode
bulk job should be closed, even when it failed
make sure that data (in Sync mode) is always written in UTF-8
now Bulk API is much more aggressive and runs several queries in parallel
initial config for akka log
make file name slicing more reliable

also added a debug info in case if it still fails
when lastRunOutputFile is not defined no need to fiddle with lastQueryProps
updated unit tests for lastRunOutputFile handling
update "lastQueryProps" tests
use provided Extension value for Document (still have to guess extension for Attachment and ContentVersion)
continuous improvement of user friendliness of exceptions

when known/recoverable exception happens do not scare user with stack trace and suggest remedies when relevant
singletons are evil - extract Config in a real class which can be instantiated
handle "ApiBatchItems Limit exceeded.'" and switch to Web Service API mode