Add missing implicit request to a few common templates
Add secure assets property to config files
Add secure assets plugin

Assets plugin is now passed the secure and insecure configuration
properties. The secure version of the plugin will use the former when
it constructs asset paths.

The corresponding static.path property appears to be unused in the
application but a similar approach may be required if statuc
components start to get added to common.
Identity project now uses secure assets plugin
Merge pull request #1665 from guardian/secure-assets

Secure assets can be enabled via SecureAssetsPlugin