WIP Name parameters support multiple values

- WIP `parameter_fields` displays two inputs;
  TODO replace it with a + button, and restrict to
  params with repeat:true
- `named_parameters` stores/returns an array of
   values instead of a single value
- `request` uses "traditional" param serialization
  to handle multiple params with the same value
  (prevents adding [] to their name), and handles
  multiple values for FormData
WIP First-pass at UI for repeatable

- Needs tests
- Needs remove and new html to be refactored
UI for repeatable
Style color of add/remove icons, add example raml
Merge branch 'master' into features/support-parameters-with-repeat-true-59453416

Conflicts:
	app/scripts/controllers/try_it/named_parameters.js
	app/views/parameter_fields.tmpl.html
Fix layout of try it
Fix test (selector changed)
Fix file uploads for repeatables
Merge branch 'features/support-parameters-with-repeat-true-59453416'