Added missing toggle for left button and right button. Fixed right
button icon setter.
Added dups of the stylebox for the line edit, as well as storing
original left and right content margins.
Updated resize to add to the content margins for left and right,
depending on if we are creating a left button, or right button.
Ensure that Button is a true flat button, with StyleBoxEmpty.
Added to spacer and container the mouse filter ignore, so that the text
field doesn't get covered by invisible controls.
