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.
@Turini I tried to use `Alternative` and `Priority` but only works with your last suggestion. I'll push a commit with this change.

Another point: which release you think we can drop `ServletBasedEnvironment`, since this class is not necessary from now?