update HTTP caching #93
                
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Refers to issue #70.
Major changes in
CacheFilter.java, implemented 1, 2, 3, 4, 5 (partial), 6, 8, 9.(Implement 6 evolves with parts of 1 and 4 so they need to be done as well)
No test has been added/updated so far, so running the test will fail since the cache has different behaviors.