add warning about changing form ID (Case:54209)
Merge pull request #64 from dimagi/warn-change-form-id

add warning about changing form ID (Case:54209)
fix issue with multiple xpath references (Case:38272)

if you had a logic condition with multiple node references and an
invalid reference was followed by a valid reference the error message
for the invalid one would never show up.
Merge pull request #65 from dimagi/multiple-xpath-references

fix issue with multiple xpath references (Case:38272)
Merge branch 'master' of github.com:dimagi/Vellum into multimedia-support