Adjust size and position of line and toolbar

UIToolbar seems not to respect the height resize option. Thus, it needs
to be done by hand.

The line is initially placed at a half point from the top. When the
super view height changes, the line is placed on an integer point. Thus,
the line is placed at a half point when laying out the subviews.
Messages.app doesn't tweak the caret
Manual scrolling is no longer needed
Adjust text view position and behavior