Added/removed dependencies, moved BasicInstrumentation to subpackage, added tests for InstrumentingInterceptor, removed instrumentationmetricSetLoader

- Added compile dependency on slf4j
- Added test dependencies on Mockito and Assertj
- Removed dependency on Guava (one class, Preconditions, is too little to
  depend on the whole library)
- Moved BasicInstrumentation to same package as InstrumentingInterceptor
  for clarity/prettyness of the project (hear, hear :> )
- Removed InstrumentationMetricSetLoader and switched to creating new
  instance of BasicInstrumentation on every call - creating well working
  cache for instances of Invocation is tricky because that class doesn't
  override .hashCode() and using only the method name (without the
  arguments) is pretty error-prone. Using the types of arguments in metric
  name might come next, but is not yet implemented. Honestly, considering
  the place where this projects is, it is not really that critical to
  reuse everything as I expect most of the execution time will be spent
  on waiting on the database anyway.