Transaction Module

Added a save button for bill which will save all information about the bill in the database. 
Currently only feedback is an alert saying Success, will do a redirect once the page to update bill is created.

Link customer id to the bill. This is optionnal, but if no user is linked, the bill must be paid in full now.
Also adds a transaction with the full amount if requested

Added more information to the list of bills like total amount, total paid and user linked to the bill.

Can open and close bills

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Shouldn't a PUT to bill directly create a bill?