Fix loading templates in config/ directory

The fixes introduced in #4235 and #4411 do not take into account, that a
template JSON in the config/ directory includes a template name, as opposed
when calling the Put Template API.

This PR allows to put both formats (either specifying a template name or not)
into files. However you template name/id may not be one of the template
element names like "template", "settings", "order" or "mapping".

Closes #4511