Allow users to select and save the preferred duo device and method, depending on availability in the duo account. A default enrollment URL is provided and adjusted if returned by the duo API. This allows auto-enrollment if enabled by the administrator.
Closes#594. Closes#1039.
This change implements yamllint and adjusts all yaml files to abide by our linting setup. This excludes config.template.yml as this will be done in an alternate commit.