Email plugin now functions more like the upload plugin. Users can go to the plugins page, click on the settings cog for the email, and switch between providers or change settings. The default provider is strapi-email-sendmail. Extra providers can be added by installing strapi-email-mailgun or strapi-email-sendgrid.
Added basic support for using Mailgun and Sendgrid (as opposed to the Sendmail) package in the email plugin. Configuration is done in plugins/email/config/settings.json