new get method

i've created a new get method similar to Properties.html#getProperty(String key, String defaultValue) to return a default value in case the key isn't set in properties file (so we don't need to try-catch when we know the value may not be set).

i've also renamed a DefaultEnvironmentTest class to ServletBasedEnvironmentTest since it was testing only ServletBasedEnvironment actually.

what do you guys think?