Upgrading version to 3.7.2-dev
optimize images
Update bower.json

Fixed path to dropzone.css
Add file type case insensitive.
More flexible previewTemplate (optional fields)

Let previewTemplate have zero or more
elements that represent data - filename, size, etc.
This will in effect make all fields optional.
Trim preview template so that createElement doesn't pick up an empty text node rather than the container.
Updated gruntfile description.
Dropzones are properly stored in the element again.

Fixes #346