UI: Fix aligning labels with other buttons.
This patch revert D6925, it was aligning the label with the checkboxes,
but after changing the checkboxes it doesn't help anymore.
In the following (old) image, the second label has an unnecessary offset.
Now the UI_BUT_NO_TEXT_PADDING flag is used to remove the extra padding.
There is still pixelsize offset (thickness of the outline) so that the text does not stick out visually,
if the outline of the button does not contrast with the background.
This also adds (intentionally) pixelsize padding for checkboxes text.
The text looks too close to the checkbox at 2x scale,
it looks less than the space between words, which is not good.
Some examples before and after:













