Set up scons build system

- In its current state, it produces a valid, launchable Mac application package, though one that's not redistributable (relies on system-installed libraries)
- Partial support is already in-place for a Windows build

test/SConscript

@@ -0,0 +1,8 @@
+
+Import("env platform party_classes common_sources")
+
+test_sources = Glob("""*.cpp""") + Split("""
+	#src/scenedit/scen.fileio.cpp
+""")
+
+test = env.Program("#build/bin/boe_test", party_classes + common_sources + test_sources)