Clean gradle dependencies

* Clean dependency versions managed by Spring IO Platform
* Temporarily use a non-platform fixed version of Spring Framework
Upgrade IO Platform and Boot

* Spring IO Platform 1.0.3
* Spring Boot 1.1.9.RELEASE
Move logging conf and clean security ignored paths

Logging configuration has been moved to application.yml.
Update security ignored paths with:
* front-end libraries located under "/lib"
* "/error" which is now ignored by default by Spring Boot
Configure Tomcat for deployment behind proxy

Spring Boot 1.1.7 now requires application to explicitely configure
`x-forwarded-for` and `x-forwarded-proto` headers in Tomcat
configuration. By doing this, Spring Boot will configure Tomcat's
`RemoteIpValve`.

This configuration is required for CloudFoundry deployments, when using
a front-end proxy such as CloudFlare's CDN+SSL.
Upgrade gradle
Upgrade to Spring Boot 1.2