Revert "Revert "Merge pull request #101 from dimagi/cleanup-is_excluded""

This reverts commit 261deff2308d49c36c69fd18630ba3f607968bd3.
have extract_case_blocks look only in an xforms `form` property
further clean up extract_case_blocks and rename helper to is_device_report
refactor extract_case_blocks to look as simple as it is
further cleanup of extract_case_blocks
Merge branch 'master' into cleanup-is_excluded
Merge pull request #103 from dimagi/cleanup-is_excluded

clean up extract_case_blocks