Gateway caching

Caching implemented with 2 Zuul filters:

• CachingPreFilter: reads cache and fill response if URI found in cache
• CachingPostFilter: stores response into cache using URI as key

Cache name uses service id.

We should take into account whether the response is gzipped.

Define an API to manage caches

Maybe on top of gateway routes.

• GET /api/gateway/routes/[serviceId}/cache returns cache information (# elements, hits, configuration, ...) if any
• POST /api/gateway/routes/{serviceId}/cache/clear clears cache

Add tests and look at closing connections

spring-cloud/spring-cloud-netflix#1196