improve cc/bcc ui layout

[tomholub]

The cc/bcc UI on compose screen is disorderly. Let's follow what Gmail app does more closely - they do it well:

• instead of Add Recipient placeholder, let's put To label to the left of the input that stays there
• Similarly for cc and bcc when we expand it. Add cc and bcc to the left as labels
• Let's auto-collapse all of this, only showing the email bubbles, when user switches to subject or body (lost focus)
• Let's re-expand the recipient area when user taps on the collapsed rendering

This way, we no longer need to have Add Recipient, Add cc Recipient, Add bcc recipient placeholders which take up a lot of space, each occupying own line. When user adds a few recipients, it quickly overwhelms my small screen (12 mini) whereas on Gmail app, it's comfortable.

Originally posted by @tomholub in #1381 (review)

[tomholub]

@ioanmo226 you've been self-assigning other issues, but I'd need you to do this particular one with priority - that's why it was the only one I've assigned you until done. Thanks!