Everywhere: Add component declarations

This adds component declarations so that users can select to not build
certain parts of the OS.

Userland/Applets/Audio/CMakeLists.txt

@@ -1,3 +1,9 @@
+serenity_component(
+    Audio.Applet
+    REQUIRED
+    TARGETS Audio.Applet
+)
+
 set(SOURCES
     main.cpp
 )

Userland/Applets/ClipboardHistory/CMakeLists.txt

@@ -1,3 +1,9 @@
+serenity_component(
+    ClipboardHistory.Applet
+    REQUIRED
+    TARGETS ClipboardHistory.Applet
+)
+
 set(SOURCES
     ClipboardHistoryModel.cpp
     main.cpp

Userland/Applets/Network/CMakeLists.txt

@@ -1,3 +1,9 @@
+serenity_component(
+    Network.Applet
+    REQUIRED
+    TARGETS Network.Applet
+)
+
 set(SOURCES
     main.cpp
 )

Userland/Applets/ResourceGraph/CMakeLists.txt

@@ -1,3 +1,9 @@
+serenity_component(
+    ResourceGraph.Applet
+    REQUIRED
+    TARGETS ResourceGraph.Applet
+)
+
 set(SOURCES
     main.cpp
 )