Parts interface for returns

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extra : source : 3859ee9dbb11c1d55408c5e8b2d5c4cb55b79b6e
Invoice changes for product returns, on the db interface level.

--HG--
extra : source : 0e631ddf056d777b3a0d6e20533a8bcd95d40859
UI components for returns

--HG--
extra : source : 25b5ad9e63c7ca261f9c1279a4b463ee957975ae
Returns fixes and menu

--HG--
extra : source : e4141f82d771cf4838175c35530d3d619be81d20
Menu added to Pg-database.sql

--HG--
extra : source : 19887d67bad9c3298537c83b1704731c1dde487b
Final fixes for returns.

--HG--
extra : source : d9940e1b206b5508f298f2a81a222c1ef0fba81a