Start to introduce caching

- [x] Add caching infrastructure
- [x] Cache blog file for index
- [x] Add hit/miss header
- [x] Have file system and memcached support
- [x] Cache queries
- [ ] Test caching queries
- [ ] Add unit tests for caching
- [ ] Get travis to test memcached
- [ ] Test memcached
- [ ] Before deployment add new parameters to parameters.yml