Update to nomlib's latest API on feature/GUI branch
Fix a few compile errs due to nomlib API changes

  Note that these modifications are non-functional; game crashes upon
execution.
Update to nomlib's latest API on feature/GUI branch

* This commit fixes the previous non-functioning modifications that were made.
Rename of GrayWindow to GrayFrame
Update codebase to latest changes in nomlib dev branch

* Introduce Card::get_id_string method.

  nom:PlayState:
* PlayState: Phase out usage of debug_text & info_text
* Rename updateMessageBoxes to on_update_info_dialogs.
* Use compact nom::Gradient initialization.
Update codebase to latest changes in nomlib dev branch
ContinueMenuState: Experimental implementation of nom::QuestionDialogBox
Update codebase to latest changes in nomlib dev branch

(See also: nomlib commit #9ab6ae6585a0649acedb8897343845235b462cfa)
Update codebase to nomlib's latest API on feature/GUI branch

* nom::Gradient API changes; introduce std::vector<nom::Color4i>
support.
Test out QuestionDialogBox interface

See also: nomlib's feature/GUI branch.
Update code to latest API in nomlib's feature/GUI dev branch

* Introduce customized logging category levels; this significantly
helps separate the run-time logging output between nomlib & the
game.

* Remove NOM_DEBUG_TRACE & co variables; these have been phased out by
moving to run-time control of logging (via SDL2 logging facilities).

* Use the appropriate logging categories for all NOM_LOG_TRACE calls
made in the project.

* Initialize / optimize logging priorities to only show game state
entry/exit traces.

* Replace nom::Cursor inheritance with nom::AnimatedSprite; this
entailed phasing out the x & y method helpers, along with a
rename of the ::position method to ::cursor_position so that
we could take advantage of the existing ::position method available to
nom::AnimatedSprite.

* Update GUI subsystem code to the latest feature/GUI dev branch
API of nomlib; everything is functioning 100% as of this point and
time, AFAIK, less & except the noted FIXME regarding absolute &
relative window coordinates of the parent (top-level) GUI window
objects (for nom::MessageBox objects).
Fix widgets positioning issue
Partial fix for using scale2x, hq2x algorithms

* Game.cpp: Remove setting default log level for
NOM_CATEGORY_APPLICATION; this is already done for us within nomlib.
Update code to latest API in nomlib's feature/GUI dev branch

* Remove calls to SpriteBatch::update; this is now handled
internally, and thus has been put under protected scope.
Rename UIEvent to GUIEvent

* Fix namespace conflict with nom::UIEvent.
Refactored audio subsystem (it is now an optional component)
Update code to latest API in nomlib's feature/GUI dev branch

* Update NOM_CONNECT_UIWIDGET_EVENT syntax for callback methods
* Change UIEvent pointers to UIWidgetEvent references.
Rename nom::Text::Alignment to nom::Anchor