Force UTF-8 encoding on file contents

`Base64.decode64` returns a string with encoding of `ASCII-8BIT`. Some linters
will try to write the file. If a file contains weird characters, an error will
get raised, like:

```
 Encoding::UndefinedConversionError: "\xE2" from ASCII-8BIT to UTF-8
```

Related error:
https://app.getsentry.com/app20126465herokucom/production/group/33706905/
Fix exemption check

* Check failed when more than one org was added. This change fixes that.
Configure Redis using redis-db defaults

* This commit implements a change suggested by @lunks in
  https://github.com/thoughtbot/hound/issues/444
* Remove Redis configuration in favor of redis-db's default configuration
* Reference: https://github.com/redis/redis-rb#getting-started
* Remove references to `REDISTOGO_URL` environment variable
* Note: Prior to merging and deploying this commit a `REDIS_URL`
  environment variable should be set on Heroku
* https://trello.com/c/AlmhdrFd/399-change-redistogo-url-environment-variable-to-redis-url
Start a FAQ page

* Add a HighVoltage page at `/faq`

Minor:
* Move styles for anchor tags from `_base` into the more specific `_header` where it used

https://trello.com/c/h9zfaC9l/386-add-an-faq
Suggest using Rubocop locally instead