Avoid various uses of html_safe

We can avoid using `html_safe` in various circumstances, through alternative approaches like i18n keys ending in `_html` or using `safe_join` to avoid converting via unsafe string types.

The `_html` keys approach only work for ActionView helper version of `t`, not the base `I18n.t` method.

app/controllers/users_controller.rb

@@ -344,7 +344,7 @@ class UsersController < ApplicationController
       flash[:error] = t "users.confirm_resend.failure", :name => params[:display_name]
     else
       UserMailer.signup_confirm(user, user.tokens.create).deliver_later
-      flash[:notice] = t("users.confirm_resend.success", :email => user.email, :sender => Settings.support_email).html_safe
+      flash[:notice] = t "users.confirm_resend.success_html", :email => user.email, :sender => Settings.support_email
     end
 
     redirect_to :action => "login"