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 think waiting until 4.2 would be enough. What do you think?