Provide a way for the Wonder Frameworks to report their version code

Provide a way for the Wonder Frameworks to report their version code.

The actual String version is plucked from the "CFBundleShortVersionString" value in a new "Info.plist" file, added for the purpose to the ERExtensions framework (which will be added to any app using Wonder).  In addition to providing the static method ERXProperties.wonderVersion(), the Property "er.extensions.version" is also set to the same value.  Since this method first appears in version "6.0.1" of Wonder, a failure to determine a version is reported as version "6.0.0".