[TEST] Left '.' as it is in REST suites and sections titles (was previously replaced with '_')

With JUnit up to 4.10 there's no way to distinguish between what's shown in IDEs and test ids that need to be unique. A test Description is identified by just a string, that needs to be unique and is shown by IDEs. IDEs have slightly different behaviours when it comes to showing tests and suites titles. Some IDE (e.g. IntelliJ) strips the description on '.', which is why the '.' was replaced in the first place, in order to obtain the same behaviour on all IDEs. On the other hand the information printed out by RestReproduceInfoPrinter was wrong as the file path contained a '_' instead of a '.', which made the string to reproduce a failure useless in some cases. At the end of the day it seems better to just keep the dots and accept slightly different behaviours that are IDE dependent.
[TEST] Added check: test section names must be unique in the same REST test suite
[TEST] Replaced File.separator with '/' as REST test suites can be loaded from classpath, where '/' is needed
[TEST] Added params validation according to REST spec and check whether body is supported or required