Add basic BetaProgram feature.

services/web/app/coffee/Features/BetaProgram/BetaProgramController.coffee

@@ -0,0 +1,29 @@
+BetaProgramHandler = require './BetaProgramHandler'
+UserLocator = require "../User/UserLocator"
+Settings = require "settings-sharelatex"
+logger = require 'logger-sharelatex'
+
+
+module.exports = BetaProgramController =
+
+	optIn: (req, res, next) ->
+		user_id = req?.session?.user?._id
+		logger.log {user_id}, "user opting in to beta program"
+		if !user_id
+			return next(new Error("no user id in session"))
+		BetaProgramHandler.optIn user_id, (err) ->
+			if err
+				return next(err)
+			return res.redirect "/"
+
+	optInPage: (req, res, next)->
+		user_id = req.session?.user?._id
+		logger.log {user_id}, "showing beta opt-in page for user"
+		UserLocator.findById user_id, (err, user)->
+			if err
+				logger.err {err, user_id}, "error fetching user"
+				return next(err)
+			res.render 'beta_program/opt_in',
+				title:'beta_program_opt_in'
+				user: user,
+				languages: Settings.languages,