[proposal] change currency mechanism

[ashish173]

Right now we are provisioning a store with a default currency of USD. This is a good approach for now. All the products which get created use this currency.

After this changing the store currency would not be possible for now.

To allow this to happen we'll need certain mechanisms in place.

Upon change of currency:-

1. Change all the currency of all the entities in the system which store the currency.
2. Also support the exchange rate while converting. If chosen by user.

developing...