make config check for new Theme bundles. refs #1935
correct display of preview image
Merge pull request #2040 from craigh/themefix

make config check for new Theme bundles. refs #1935
do not load Bootstrap in non-admin controller for non-bundle themes. refs #2041
Merge pull request #2043 from craigh/themecompat

do not load Bootstrap in non-admin controller for non-bundle themes.
fix BC concerns. refs #2043 ping @cmfcmf
fix BC concerns - part 2. refs #2043 ping @cmfcmf
Updated error message, refs #2044