Add system property and env variable resolving to property prefix and suffix

This change adds system property and environment variable resolving to PropertiesComponent's propertyPrefix and propertySuffix. This makes custom PropertiesParser unnecessary in the use case stated here: https://issues.jboss.org/browse/MR-854.

Also renamed org.apache.camel.util.FilePathResolver to SystemAndEnvPropertyResolver as its functionality has nothing to do with files.

Finally, fixed unintuitive behavior of override properties not being used if there are no properties loaded from elsewhere. Now you can use override properties to put properties into PropertiesComponent in plain Java (handy in unit tests or in the SCR world, for example)