iOS Beta: OMEMO and Push

There is a new iOS beta with the current OMEMO code and UI enabled. I am still testing this and there are more UI elements that need to be added/adjusted. Please let me know how it works for you.

I have also worked on push support. I am moving towards improved push reliability at the expense of older servers that do not support it. This is largely a desire on my part to remove stale code and reduce complexity. Push has seen sufficient adoption that I believe this should not be a problem for most people.