Feature: add array support to config.angular_templates.ignore_prefix

This change will make it possible for the `config.angular_templates.ignore_prefix` option to take an array of values. Each value will be ignored if it is at the start of the templateUrl string.

For example: `config.angular_templates.ignore_prefix = %w( templates/ legacy/templates/ )` means your templateUrl paths can be shortened if you have more than one template folder:
`'templates/nav_bar.html'` => `'nav_bar.html'`
`'legacy/templates/old_alert_window.html'` => `'old_alert_window.html'`

`config.angular_templates.ignore_prefix` still supports a string option for backwards compatibility.