Make collapsing optional

For #55 - adds an option to enable/disable the collapsing behavior of fieldsets

Note: This could be considered a "breaking change", as your existing Archetypes will now have collapsing disabled, since I added the option as "Enable Collapsing".  I could add some checks to enable when its blank, but I figured its not worth it since we're still in alpha.  Happy to change if anyone thinks otherwise.

### Config ###
* Add option to view
* Set default to enabled for new datatypes

### View ###
* Prevent collapse/expand depending on config option
* Add class when enabled, hide carets when disabled

### CSS ###
* Revert to normal cursor when collapsing disabled

* Note, this is a breaking change - you'll need set `Enable Collapsing?` to `true` on any existing Archetypes to retain the behavior.