* Support specifying payment method through apps
closes#1525
This is great if you want to offer items with an incentive to use a specific payment method without messing with the rates.
For example, you can have `Item A` which costs 25$ and your store is configured for USDT and BTC. You can create two items, with different prices, where Item A costs 20$ if you pay with bitcoin or 25$ if you paid in dirty fiat pegs
* make code cleaner
* Add Test
* fix test
* fix test
* Fix: Only USD currency with 2 decimals were properly handled for tips
* Fix: All PoS apps would were sharing the same basket
* Fix: Currency formatting was not using server side information
* Fix: Various bug of formatting for decimal 0 and more than 2.
Modal cart, remove items, checkout
Fix removal and adding of cart items
Improve cart UI
Add cart bundle, remove unused js files from the view when cart isn't used
Do not enable cart by default
Do not put modal into the view when the cart is disabled
Escape js properties
Work with amounts as cents
Make animation speed look constant
Enable tips in the cart
Fix cart UI
* Preserving title with custom amount
* Custom button texts for complete localization
* Update tests, now checking custom amount description and button text
* Support for Custom CSS in POS
* Tweaking appearance of custom amount card
* Allowing POS items to have custom amounts, good for donations/tips
* Prepending currency symbol in POS
* Fixing regression, thanks unit test
