Add types for prototype params and templates

This commit will fix #116 by introducing two new constructs to the
prototype specification schema:

1. Mandatory types for prototype parameters. This lets us accept bare
   words on the command line, and then "do the right thing" when
   emitting JSON or Jsonnet.

   For example, say a template produces a `core.v1.Service` that exposes
   a port with a `--targetPort` flag. When the user passes a number
   (e.g., `80`) in, we should _not_ put quote marks around it, since we
   want to expose port `80`. When the user passes a string (e.g.,
   `"nginxPort"`), we _should_ put quote marks around it, to denote that
   we're exposing the port with that name.

   In order to do this, we need to know they "type" of the parameter (in
   this case, `NumberOrString`).

2. Mandatory template types. A template can have a JSON, YAML, or
   Jsonent flavor, and we default to using Jsonnet. This is useful
   mostly to make type parameters less error-prone (since one set of
   parameters corresponds to one set of templates), but it also
   significantly de-bloats the output of commands like `search`, since
   one fully-qualified name can correspond to multiple flavors of the
   same template.