Add additional local template and or script files when launching a new stack

Summary
========
Add additional files section to “launch stack” form

Motivation
========
Match Openstack Heat features:
1. Several template files would be beneficial to user, having more customization and control.
2. Templates would relate to each other, allowing use of custom types as stack resources.
3. User could upload bash scripts.

Description
=========
1. Pressing on "Add Additional File" will allow the user to select multiple local files.
2. Each file will get a column which contains the file name, upload path and a delete button.

Mock
====
http://invis.io/C43EVKTYU

Outside Dependencies
==================
API calls are supported on OpenStack Heat (base API).
request example:
{
  “template”: “{}”
  “files”: {
    “scripts/start.sh”: “# CONTENT”,
    “scripts/stop.sh”: “# CONTENT”,
    “README.txt”: “# CONTENT”,
    "templates/nested_type.yaml": "# CONTENT",
  }
}

Doc Impact
=========
1. Add explanation for the new form fields
2. Add explanation for the new flow