Userpoints Payment improvements

A patch is attached which improves the following in uc_userpoints_payment:

• branding of points during checkout (for example, to rename "points" as "store credit")
• option to hide display of userpoints amounts at checkout (added for a client who did not wish the user to know exactly how many points they had)
• round prices up to the nearest exact point value, rather than rounding to the dollar value (fixes #512278: User points do not get substracted when using as payment)
• improve translations (including #642368: uc_userpoints_payment module string for translation)
• replace "dollars" with "currency"
• link back to orders from userpoints user and administration pages (requires Userpoints patch from #698872: entity_type hook always displays operation as "Array")