re-added image references
fixed repeat buttons in default/formhub themes
fixed broken tablewidget (due to SFI-prompted xsl changes)
moved some stuff to core/print, added .no-print class
fixed table widget after SFI-grid-prompted xsl changes
prevent Travis from attempting to build branch with private submodule
Merge branch 'master' of https://github.com/MartijnR/enketo-core into SFI