[ENH] Module product_pricelist_fixed_price:
    - Backport improvements from 7.0 branch
[FIX] Module product_pricelist_fixed_price:
    - No Price Computation group in 6.1
[MIG] Module product_pricelist_fixed_price:
    - Migrate data from previous versions of module.
[FIX] flake8 fixes for product_pricelist_fixed_price
Change reference to non existing menu, and some pylint changes
Some more fixes to pass travis. Do away with print statements.
Merge pull request #18 from NL66278/6.1

[ENH] Module product_pricelist_fixed_price: