CMFCategory: fix several *TitleItem* & *IdItem* getters

'display_id' expects a property name and 'display_method' a method name
Amount Generator: make lines sortable with float indices
Amount Generator: make first matching line mask other with same reference

This is implemented by first changing Composition so that a model can
define several lines with same reference, masking inherited ones.

There is actually no compatibility issue, because previously, the result would
have been undefined (composition only keeping a random line).
Make Resource.getPriceParameterDict return extra mapped values

For example, Sale Supply Lines/Cells can be customized to return values for
the caller of Movement.getPriceCalculationOperandDict