Update PageFinder to support matching of runtime values from API variables. Also update InputfieldSelector to support them with use of the "custom (field=value)" option (which can also be used for other things too).
Add multi-language support to file and image descriptions.
Add support for parsing [api_var.property] in the value portion of selectors.
Add a whitelist to the last commit so that parsing of API vars is limited to just: page, user, session, for now. We'll add more later or make it configurable.