Refactor qmake SUBDIRS structure

The big swift.pro is refactored by the correct usage of SUBDIRS
template. The following additional changes are made:
- Removed '_' from all targets and folder names
- Aligned parent folder and target name

refs #461

src/src.pro

@@ -0,0 +1,39 @@
+load(common_pre)
+
+TEMPLATE = subdirs
+CONFIG += ordered
+
+SUBDIRS += blackmisc
+
+contains(BLACK_CONFIG, BlackSound) {
+    SUBDIRS += blacksound
+}
+
+contains(BLACK_CONFIG, BlackInput) {
+    SUBDIRS += blackinput
+}
+
+contains(BLACK_CONFIG, BlackCore) {
+    SUBDIRS += blackcore
+    contains(BLACK_CONFIG, BlackGui) {
+        SUBDIRS += blackgui
+        contains(BLACK_CONFIG, SwiftGui) {
+            SUBDIRS += swiftguistandard
+        }
+        contains(BLACK_CONFIG, SwiftCore) {
+            SUBDIRS += swiftcore
+        }
+        contains(BLACK_CONFIG, SwiftData) {
+            SUBDIRS += swiftdata
+        }
+        contains(BLACK_CONFIG, SwiftLauncher) {
+            SUBDIRS += swiftlauncher
+        }
+    }
+}
+
+contains(BLACK_CONFIG, XPlane) {
+    SUBDIRS += xbus/xbus.pro
+}
+
+SUBDIRS += plugins