English text changes

I was giving your app a spin, and I found that these two strings confused me a little bit.

`remove_contact_text` has a question not followed by a question mark, and I had to read it a couple times to figure out what it meant.


I found the current `send_failed` text to be a bit confusing. When I read "unsuccessful delivery", part of me sees it as "successful delivery" and it make me confused as to why it's an error. I think "delivery failed" is clearer and easier to read at a glance.