[FIX] point_of_sale: add scrollbar when there are too much payment methods
[IMP] point_of_sale: adding visual feedback when clicking on buttons
[IMP] point_of_sale: add an invoice button (does nothing yet)
[FIX] point_of_sale: fixing potential timeout issues when sending orders over bad connection
[IMP] point_of_sale: ...
[FIX] point_of_sale: correctly set the customer on the order
[IMP] point_of_sale: the invoicing should now work reliably and validate the orders
[IMP] point_of_sale: add a configuration option to enable invoicing from the Point of Sale (enabled by default)
[MERGE] Forward-ported lp:~openerp-dev/openobject-addons/7.0-pos-improvements-fva (using -r 8946..8955).

This branch holds several improvements for the point of sale. However it cannot
be merged into 7.0 because a new column is added. As this branch has proven to
be correct, it is forward-ported into trunk.
[FIX] point_of_sale: LocalService -> signal_ validation
[IMP] point_of_sale: ported the proxy to the new routing api
[MERGE] from upstream
[IMP] point_of_sale: reduced the weighting probe interval, and put a non zero default value for easier testing
[MERGE] point_of_sale: various fixes and improvements: invoicing support, snappier scale, and a more robust order sending