Enable to set template by name (instead of id)

[felbalart]

Currently the template is specified using the method set_template_id with an ugly id, E.g. f49189763-ed30-123a-6lek-35221de331e5

It would be great and more human-friendly to be able to use the template or version's name.

As this feature is not provided by sendgrid-ruby gem, it probably requires to query the template ids by name using bare Sendgrid API

This feature was once developed, but later removed in this commit

So the issue might be solved using a similar approach, though the get id from name logic seems misplaced in the Deliverer class.