Default to default.template.toml, fall back to template-schema.js

[benloh]

template-schema does not correctly generate a _default.template file.

The top level parameters do not quite match up.

[benloh]

We should be able to generate a new
default.template.toml file from the schema. That would ensure that
default template is up to date.

There isn't a single-button UI for this
currently, but you CAN basically do this by:

1. Start NetCreate with a new db, e.g. ./nc.js --dataset=newdefault
2. Clicking "New Template" on the "More... > Edit Template" tab.
3. Clicking "Save Changes"
4. Copy the file to netcreate-2018/build/app/assets/templates/
5. Renaming the saved template to _default.template.toml