Merging ServletBasedEnvironment with DefaultEnvironment

As described in #811.

VRaptor was designed to works with Servlet environment, so there is no reason to `DefaultEnvironment` lives without `ServletBasedEnvironment`. Almost all tests inside `DefaultEnvironmentTest` is duplicated in `ServletBasedEnvironmentTest` too.

So with this pull request I merged both classes, and did a some refactor to make some improvements like loading properties file without recreating unnecessary instances. All instances creation are moved to `PostConstruct` method, and more.
I'll remove this test because makes no sense. There is no way to test this case because `Class.getResource` method can't mocked. Debuging this test, `env.getResource` returns null, and because `Class.getResource` returns null too, we are getting a green bar. So `assertThat(null, is(null))` is true, but technically this test has no effect. We aren't test anything.