Revert to Configuration::CONSTANT syntax for getting config values

If general.yml and test.yml are present in the config directory, the
config is overridden to use values from those files instead (assumes
that the file lib/themes/hampshire/configuration.rb is present)
Updated README to include a section about overiding the Configuration model
Merge branch 'issues/47-reimplement-config-lib' into hampshire
Create theme version of show template, split out partials
Use config to switch comments and alerts off
Add config and partial for social media sharing
Fix bug - authority.applications_per_week breaks in Postgres
Remove references to scrapers from authority view, calculate received applications per week
Fix config override bug