Nested collections path problem when creating new content

[andreasbalevik]

Content types using nested collections has some problem when creating new content.

The path field does not get updated with title resulting in error message. Path is pointing to the parent directory. But we want to create a new page under the parent.

Now path and title needs to manually be set for the page to be created.

[andreasbalevik]

Added https://github.com/netlify-labs/netlify-cms-widget-parent which enables a drop-down list for choosing parent directory. But this is a experimental widget.. but it works.

Implemented in #44