QIF export refinement

Try best effort to keep splits memo. The split whose account to chosen as group account will lose its split memo. Now we try to pick one without split memo as group account.

Sort all transactions by time.
Replaced hard-coded account name
Merge pull request #204 from fefe982/dev-qif-export

Sort QIF transactions by time. 
Added optimizations to keep the split memo in the export whenever possible