Attempt to add imports for Classes from java.lang

If you run a sphinx build with -n you receive errors for each reference type
that isn't mentioned in an import directive, or defined in the javadoc_url map
This produces many errors for Classes like String etc. and too many of
these prevents readthedocs from completing the build of your project.  This change
change attempts to detect use of classes from java.lang by adding an import
for any ReferenceType that wasn't explicitly imported.  This could result in
incorrect imports since wildcard imports are ignored.