Audio: Replace SFML solution by using OpenAL directly

This is a major change in the Audio module that comes with
many changes throughout the codebase and dependency list.
The main gist is that we're finally nuking the last pieces
of SFML from the project. sfml-audio brought with itself
unneeded and big dependencies (libsndfile, libvorbisenc)
while at the same time limiting the amount of audio formats
mkxp can support (eg. we now get mp3 for free, and wma/midi
can be implemented by extending SDL_sound directly).

The increased control gained by interfacing with OpenAL directly
will also allow for easy integration of a dedicated audio
stretcher (librubberband), as well as enable us to implement
looped ogg vorbis (via the 'LOOPSTART'/'LOOPLENGTH' tags),
as required by RGSS2, in the future.

The FileSystem class has had its SFML parts removed.
Aditionally, audio file extensions to be supplemented are
now automatically detected based on how SDL_sound was
built (ie. if no mp3 support was built, mkxp won't try
to look for *.mp3 files). The final used extension
can be optionally returned by 'openRead' calls so
SDL_sound and SDL2_image can immediately choose the
right decoder.

The OpenAL context is created and destroyed in main.cpp
along side the GL context.

mkxp.pro

@@ -1,7 +1,7 @@
 
 
 TEMPLATE = app
-QT = core
+QT =
 TARGET = mkxp
 DEPENDPATH += src shader assets
 INCLUDEPATH += . src
@@ -14,9 +14,9 @@ isEmpty(BINDING) {
 CONFIG += $$BINDING
 
 unix {
-    CONFIG += link_pkgconfig
-    PKGCONFIG += sigc++-2.0 glew pixman-1 zlib sdl2 SDL2_image SDL2_ttf sfml-audio
-	LIBS += -lphysfs
+	CONFIG += link_pkgconfig
+	PKGCONFIG += QtCore sigc++-2.0 glew pixman-1 zlib \
+	             physfs sdl2 SDL2_image SDL2_ttf SDL_sound openal
 }
 
 # 'slots' keyword fucks with libsigc++
@@ -62,7 +62,8 @@ HEADERS += \
 	src/config.h \
 	src/tileatlas.h \
 	src/perftimer.h \
-	src/sharedstate.h
+	src/sharedstate.h \
+	src/al-util.h
 
 SOURCES += \
 	src/main.cpp \