BL-815: Improve previews of templates

- locate xmatter CSS correctly
- hide images with no src
Don't cut off name when creating source collection (BL-733)

Cut off was caused by BetterLabel which was to high, overlapping
the text box. We don't really need a BetterLabel here, so I
replaced it with a regular Label control.

Also anchored the text box and the HTML label that shows the path
to the right so that the full width of the window gets used.
BL-747: Handle networked drive paths in EnhancedImageServer
Merge pull request #194 from BloomBooks/handleNetworkDrives

Handle network drives
Merge pull request #193 from ermshiperete/BL-733

Don't cut off name when creating source collection (BL-733)