travis config: checkout OCA/reporting-engine
fix flake8 reported issues

Some unused symbols were removed but I had to disable flake8 on some lines,
following an advice by Lud DeMeyer:

"You should NOT remove the ‘unused variables’ in none of the
report_xls dependent modules because flake8 is not capable of understanding the
‘python name space’ trick done by report_xls."
V7 add asset management with demo & yml
add reporting_engine to 7.0 travis.yml
7.0 - fix account_asset.yml
Refactor of method create_move so that it can be extended more easily.
Bug fixes