404 page

First iteration of the 404 page, Fixes https://github.com/DoSomething/dosomething/issues/3289 

*Missing final title/copy for the default node*
You need to change tabulation settings in your editor. Drupal standart is 2 spaces. If you're using Sublime, you can add to settings:
```
tab_size": 2,
"translate_tabs_to_spaces": true,
```