"from" selector in compose not obvious -> align with Gmail behavior

[tomholub]

This "from" only shows when the user has more than one sending address (another sending alias)

Gmail makes it pretty obvious that it's "from"

Our own UI is a lot less obvious, and can confuse the user:

Todo in this issue:

• add From and To (and Cc / Bcc) to the left of the input fields
• switch order of inputs: From should be above To and others
• (maybe) From would not have to be visible in "collapsed" (unfocused) view. It's only needed in the expanded view, similar to what Gmail does