Drupal Webform: Re-enable hook_civicrm_buildForm and comment in different situations we need alterContent and buildForm to load js scripts

Better other credits area in README.

Clarify readme.

BillingBlock.tpl is gone!
JS For Stripe is now injected on appropriate pages.

Known fixes
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GitHub Issue: https://github.com/drastik/civicrm_stripe/issues/28
Ability to submit backend/offline contributions for a contact w/ Stripe.

Previous fixes
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The last commit also fixed GitHub Issue:
https://github.com/drastik/civicrm_stripe/issues/9
USD forced on recurring plans.