add new spec tests runner allowing to easily run all specs in a package as junit tests

Example of use:

@RunWith(RestxSpecTestsRunner.class)
@FindSpecsIn("specs/city")
public class CitySpecTest { }
by default save specs in src/test/resources/specs,
following the default maven convention
refactor: recorded specs saving is now part of spec API
+ change the default location where they are stored
change default location for storing recorded specs

move them to src/main/resources so that they appear as examples
FIX: api docs: 'required' information was negated
allow to record a spec in dev mode using request headers
add button to send and record a request

we still need to disable / remove the button in PROD mode where it doesn't work