Default composite separator conflicts with spatial extension

[fostermh]

While working with scheming, spatial, harvester, composite, and repeating extensions I noticed that the default separator of '-' for composite fields caused some problems. This was mostly due to the default field names in the spatial extension containing the same character. I had previously forked the composite extension and added a config setting to set the separator used on composite fields to a custom character.

Now that scheming supports this functionality directly I suggest adding a config setting to allow users to set the separator character to something other than a dash if needed. Pull request https://github.com/ckan/ckanext-scheming/pull/295 addresses this suggestion.