allow to order fractional units

[wvengen]

When buying large packages, a foodcoop may want to subdivide it. Currently, that can be done by adjusting the unit, then manually recomputing the unit_quantity and price. This could be much easier when there would be a unit_divide field, indicating in what units members can order.

This is work in progress on branch uicleanup-new-grouporder-subdivide.

• [x] support non-integer amounts in data model
• [x] include ruby-units for unit computations + configure units
• [x] add subdivision to article edit screen
• [x] reintroduce edit boxes in member order screen
• [x] support fractional units in member order screen
• [x] check negative entry in member order @wvengen
• [ ] show price/kg when sensible in member order and admin order screen (using helper) @wvengen
• [ ] unit tests for the use of unit_divide (see also foodcoops#120) @tg-x
• [ ] fix any close order and distribute issues
• [ ] integration test(s) for subdivided order @tg-x
• [ ] make balancing screen work (might work already)
• [ ] test that everything (still) really works ok

would be nice / need to do in the future:

• [ ] check that performance doesn't get much worse
• [ ] rebase on upstream (involves some changes)
• [ ] open upstream pull request - see foodcoops#209
• [ ] change confusing gray box style of subdivide box in edit article screen
• [ ] use ruby-units in Article#convert_units

[wvengen]

this is mostly done, what remains is finishing unit and integration tests

[wvengen]

This is stuck, by the way. May need a data-model redesign (see mails 1 and 2).