Permit reading CML with missing bonds.

Change-Id: I4204c49eefe685d79671cad4a4eec7c4097bffba
Fix 'retry' behavior in FileFormatDialog.

Change-Id: I0f31c9ad2f3e3bb168f9bb49655a4574eb327306
Fix multifile openbabel file readers.

These only work with files, and openbabel must open the file
itself to properly initialize streams. Currently only recognizes
VASP files, but this can be extended in the openbabel extension.

Change-Id: Id2fe8b62cb0b9abd529187c66a8bce4c1b6706ac
Merge topic 'fix-openbabel-multifile-readers' into master

160c1464 Fix multifile openbabel file readers.
ab95a773 Fix 'retry' behavior in FileFormatDialog.
5cbaed22 Permit reading CML with missing bonds.