Build: Switch to CMake :^)

Closes https://github.com/SerenityOS/serenity/issues/2080

Applications/Piano/CMakeLists.txt

@@ -0,0 +1,13 @@
+set(SOURCES
+    AudioEngine.cpp
+    KeysWidget.cpp
+    KnobsWidget.cpp
+    main.cpp
+    MainWidget.cpp
+    RollWidget.cpp
+    SamplerWidget.cpp
+    WaveWidget.cpp
+)
+
+serenity_bin(Piano)
+target_link_libraries(Piano LibAudio LibGUI)

Applications/Piano/Makefile

@@ -1,15 +0,0 @@
-OBJS = \
-    AudioEngine.o \
-    MainWidget.o \
-    WaveWidget.o \
-    RollWidget.o \
-    SamplerWidget.o \
-    KeysWidget.o \
-    KnobsWidget.o \
-    main.o
-
-PROGRAM = Piano
-
-LIB_DEPS = GUI Gfx Audio IPC Thread Pthread Core
-
-include ../../Makefile.common