Added demowallet payment API

Multiple providers are supported. Check the configuration and add a similar payment.whatever.js to add a whatever payment service.

Jira-Issue: WP-651
Fixed minor bracket issue

Jira: WP-651
fixed weird bug on android

Jira-Issue: WP-651
Merge pull request #1 from andreasbotsikas/WP-651

Added Payment API for android