Ensure consistent margins/padding with currency converter keypad

[HowardWolosky]

Fixes #87.

Description of the changes:

• Simplifies the layout of ConverterNumPad to match that seen of NumpadPanel in Calculator.xaml.
  • They now both use the same static margin ('3,0,3,3)
  • Removed two "gutter" columns that had been used for dynamic margins.

The GutterLeft and GutterRight columns were left untouched on purpose.
They are only activated when in a "landscape" width/height orientation, used to ensure that the app display is evenly split 50/50 between the input fields and the number pad.
GutterLeft gives a margin to the input field column, while GutterRight is used to ensure that the number pad column has an equal width available to it (as the numberpad is displayed in a column span that merges its column with that of GutterRight.

How changes were validated:

• Validated with a "screen ruler" that the left/right/bottom margins were the same within Volume.

• Validated with a "screen ruler" that the left/top/bottom in Volume were identical to those seen in Standard mode.
  

• Verified the margins in "wide" mode as well
  

[joseartrivera]

Looks good to me! Thanks for making this change! 👍

[mdtauk]

These converter pages should reuse the same Number Pad, and screen layout. Perhaps there should be a template page included so future additional pages will be consistent.

[grochocki]

These converter pages should reuse the same Number Pad, and screen layout.

Visually, it is the same Number Pad, no? I agree this should be one component, if it is not already.

IRT overall page layout, I think we need to consider a broader redesign of the converter interface. I touch on that here a bit here, but I think there might be an opportunity to collapse converters so instead of navigating to an entirely different page, you can change between units on one page.