GH-1969, GH-2029 Plus & Premium In App Promo's

[benstrumeyer]

• Have you followed the guidelines in CONTRIBUTING.md?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Have you added an explanation of what your changes do?
• Does your submission pass tests?
• Did you lint your code prior to submission?

• Addresses copy changes in GH-1969 and GH-2029 in the Plus and Premium Promo Modals
• Slipped in slight CSS changes that keeps the first Premium feature on one line

Tickets:

• https://cliqztix.atlassian.net/browse/GH-1969
• https://cliqztix.atlassian.net/browse/GH-2029

[wlycdgr]

2 things -

• Does the sign in link copy also need to be updated as per GH-1969?
• I remember that a bunch of the CSS decisions for the Premium modal were compromises to make sure that the modal didn't look too bad/broken across any of the languages we support - that is part of why it looks sub-optimal in English. If you haven't yet, make sure these changes don't break the layout in languages like German and Russian.