Allow overriding of default Django registration templates

The Django Admin site is before Django registration in the INSTALLED_APPS
list.  Rather than mucking with the INSTALLED_APPS order (which seemed to
have no affect anyways), it seems cleaner to use the filesystem template
loader to pick up these templates
Fix Django Debug toolbar

With nginx in place the REMOTE_ADDR field in the HTTP header is no longer
10.0.2.2, but instead 127.0.0.1
Add some empty templates for use as prototypes

Also cleans up some urls/views:
 - Removed individual mapper page view, this will be on the group settings
 - Added achievement and training pages
 - Moved other instances of group name -> group slug
 - Made all events URLs be under group/<group_slug>/event/<event_slug>
   This is needed because event slug is `unique_together` with group_slug
Merge pull request #121 from maurizi/empty-templates

Add some empty templates for use as prototypes
Attempt to resolve periodic Gulp/Sass build errors

There is no clear evidence that these changes resolve the issue, but two
sets of changes are being made to try and suppress/isolate errors:

- Only delete and recreate the `node_modules` symlink within the project
root if it wasn't already a symlink (that maps to a directory on the
virtual machine's file system). The main driver for `node_modules`
delete/recreate was to prevent a scenario where someone ran
`npm install` manually, which would lead to a `node_modules` directory
on the VirtualBox share.

A `node_modules` directory directly on the VirtualBox share is not
desirable for Vagrant users on Windows because Windows does not allow
regular users to create symlinks (`npm` produces symlinks internally
within `node_modules`).

- Bypass `scripts` mechanism in `package.js` because it does not seem to
set the `HOME` environmental properly:

  vagrant@app:/opt/app$ grep "test" package.json
      "test": "sudo -E -u nyc-trees env"
  vagrant@app:/opt/app$ npm run test | grep HOME
  HOME=/home/vagrant
  vagrant@app:/opt/app$ grep "test" package.json
      "test": "sudo -u nyc-trees env"
  vagrant@app:/opt/app$ npm run test | grep HOME
  HOME=/home/vagrant

Instead, use Ansible's `sudo_user`, which outputs
`HOME=/var/lib/nyc-trees`.

Example task to test:

  - command: "env"
    sudo_user: nyc-trees
    register: xyz

  - debug: msg="{{ xyz }}"

(Output not provided because there is a lot of it.)

Attempts to resolve #117.