Silverstrap 3.0.0 released

Silverstrap is a theme for SilverStripe based on the Bootstrap front end framework.

The 3.0.0 release is a big refactoring that pursues SilverStripe 4 compatibility. As such, many things have changed from the previous releases. For SilverStripe 3 compatibility please refer to the ss3 branch.

• Move and refactor templates into the proper SilverStripe 4 location.
• Fix Form.ss escaping and position.
• Add support for external links in NavBar.
• Update templates for silverstripe/silverstripe-blog.
• Add axllent/silverstripe-enquiry-page support.