[iOS] Add EULA link into the application

[nizmaylova]

Add EULA link into the iOS mobile application.

Note: Current edX app from store is shown in the attachment

Currently, the open edX app shows EULA paragraph and other relevant links within it on the Register screen. We need to add the paragraph on the Sign-in screen and match the copy accordingly. Below are the examples.

Open edX Register Screen	Prod edX Register Screen	Prod edX Sign-in Screen
The EULA paragraph needs to be moved below the optional fields CTA. We also need to add a checkbox for getting marketing consent on this screen as seen in the screenshot on the right (Prod edX Register Screen).		We need to replicate the copy and implementation highlighted above on the sign in screen of the open edX app.