AURORA: Add isEmpty() to 2DA cell
Though an empty cell returns a default value, it might happen that this
value can be the same as a non-empty cell and hence there is no way to
check emptiness.
NWN: Add setter/getter to creature's portrait

Also add an initial value to creature's portrait.
GRAPHICS: Allow to change textures node in-game
NWN: Add access to nodes in ModelWidget
NWN: Nitpicky style fixes
AURORA: isEmpty() -> empty()

For consistency's sake.

See also 9b35a591a3a1c381866db12dcf1cc4fe70ae211a
NWN: Fix colour change when enabling button

When buttons were first disabled and then enabled again, the colour
remained grey. They will now change accordingly.
NWN: Handle mouse state events in Portrait
NWN: Add SetBorderColor() to Portrait
NWN: Prepare WidgetListBox to be a base class

Moving private members and variables to protected.
The goal is to extend it to a grid.
NWN: Add getSelectedItem() to WidgetListBox

This method returns a pointer to the selected item.
NWN: Add WidgetGridBox

WigdetGridBox is very similar to WidgetListBox but represents the items
in a grid instead of a list.
NWN: Fix license / copyright comment header

See 7e0da5fe776c8d3fa54c99929226df50f34ae83f and
03bafddd5a229c1dcf083a869f112892d1fccddf.
NWN: Remove trailing whitespace
NWN: Add portrait chooser in chargen
GRAPHICS: Treat FreeType's FT_Bitmap fields as unsigned

This fixes compilation for FreeType 2.5.4:
> Some fields in the `FT_Bitmap' structure have been changed from
> signed to unsigned type, which better reflects the actual usage.
> It is also an additional means to protect against malformed input.
>
> This change doesn't break the ABI; however, it might cause compiler
> warnings.

In our case, since we're using a MIN() template, it even caused
compilation to fail.

Treating them as unsigned is apparently the preferred way, so we're
always doing that now, even for FreeType < 2.5.4.
KOTOR: Add GUI buttons loading support.