Fixes #336 - removes hardcoded SMC code

Removes code specific to San Mateo County, CA.
Improve code, fix bugs, and updates specs in PR #444

- Combine all customizable settings in one file. That way, there is only one place the user needs to remember to visit to make changes. This also saves us from having to write instructions like "to change setting A, go to file X, to change setting B, go to file Y." Keep it simple.

- Load the settings file once at runtime and assign the contents of the YAML to a constant.

- Document all customizable options thoroughly in settings.yml

- Take advantage of YAML keys that correspond to Rails environments to be able to use different settings in the test environment without having to create a new file and use multiple conditionals in helpers.

- Move hardcoded content to the settings file. For example, the SMC logo was replaced by the Ohana Web Search logo, but that should have been made a customizable option. Same with the default recipients of the feedback form and the site title.

- Make feedback mailer more customizable by using values from settings file to define the recipients and email subject.

- Fix CSRF Token bug in the feedback form. Rails 4 introduced protection against CSRF attacks, but when we upgraded, we failed to test the Feedback form, which uses AJAX to submit the form. The fix was to add the token to the headers.

- Move homepage links and info box helpers out of application_helper and into their own helper modules to keep functions separate and easier to read. Refactor methods and method names to make them smaller and more readable.

- Replace partials that use uninformative variables with more readable methods that render the HTML via content_tag.

- Rename partials to match helper names.

- Simplify info box lookup by only comparing keyword with synonyms field.

- Simply info box lookup by using "custom" key for info box that uses custom template.

- Use the Rails "try" method instead of multiple conditionals (http://apidock.com/rails/Object/try)

- Document all new methods.

- Simplify calls to partials in views. ":partial =>" is not necessary.

- Update specs to match the test data in settings.yml.

- Add more specs to test the info box and homepage links more thoroughly.
Merge pull request #444 from codeforamerica/336-remove-hardcoded-smc-code

Fixes #336 - removes hardcoded SMC code
Use CANONICAL_URL env var to identify URL in feedback mailer
Removes unused filter logic from view

Removes logic for a select menu (which is unused) from filter view.
Ties into #425.