Nothing to see here, move along...
Disable logging of init methods

* Trace logging of nom::init, nom::quit.

* Info level message logging in PlatformSettings, SystemFonts,
SystemColors.
UIWidget: Clean up layout size & size policy logic

* Introduce nom::WIDGET_MAX_SIZE const var; for use with ::maximum_size
methods.

* Modify the default behavior of ::maximum_size, ::minimum_size
and ::size_hint. Note that these method calls no longer return
Size2i::null; hopefully this helps correct math errs that can
result from unexpected negative numbers.

* Initialize widgets with the default size policy of
UILayoutPolicy::Policy::Preferred.

* Introduce set_size_policy variant method (for sake of convenience).
Button: Refactor ::minimum_size && ::size_hint methods

The size dimensions returned from ::size_hint are now multiplied by a
factor of two. In short, this is for much improved visual appeal (see
comments for details). Upon err (for whatever reason) in ::size_hint, a
size of zero width & height are returned.
  The result from ::minimum_size is now always half the size returned
from ::size_hint.

* Button: Initialize the widget's size policy at construction.

* BitmapButton: Remove explicit setting of minimum size (this is
already done within the base class for us).

* BitmapButton: Add a safety net within ::size_hint when default bitmap
image is not valid; pray that Button::size_hint has better luck.

* BitmapButton: Re-implement ::minimum_size; returns the same value as
::size_hint.

* UIBoxLayout: Move the calculation of decorator's border geometry
from ::minimum_size to main widget item loop in ::set_bounds. The
resulting offsets represent the final size requirements that should
be needed by an item.
ButtonLayoutTest: Clean up much of the redundancy in the tests

* ButtonLayoutTest: Add a fourth button for testing.
* ButtonLayoutTest: Add tests for layouts that use Size2i::null dims.

* Button: Set the size policy to Minimum / Fixed when using non-NULL
size dimensions, and Preferred / Fixed otherwise. This allows us to
render a button widget with explicit dimensions even when used in a
layout.

* UIBoxLayout: Add size policy logic for Horizontal / Minimum,
Horizontal / Preferred, Vertical / Minimum & Vertical / Preferred.

* BitmapButton: Introduce ::bitmap_size for obtaining the size
dimensions of the set bitmap image.
Fix unit test failures in ListBoxLayoutTest

* ListBox: Bit of clean up the visual presentation of the text
within the widget by adding some padding (see ::size_hint, ::update).

* ListBox: Re-implement ::minimum_size; returns the same value as
::size_hint.

* ListBox: Set the size policy to Minimum / Fixed when using non-NULL
size dimensions, and Preferred / Preferred otherwise. This allows us to
render a listbox widget with explicit dimensions even when used in a
layout.

* UIBoxLayout: Fix bug in frame boundary calculations that affected the
last widget item in both the button & listbox layouts.

* ListBoxLayoutTest: Reduce redundancy by moving common code to helper
methods (alike ButtonLayoutTest).

* ButtonLayoutTest: Add a decorator for button3 (visual aid for seeing
widget bounds).