Event-driven dialog queue, story flag command, mod unit tests

Push-based event chains, runtime fixes (single end, goto lifecycle, if,
busy box, held delay, empty options, timed/animated/effect actions), the
'flag name value' DSL command, autoplay --dialogs=N, 19 mod unit tests.

manifest.json

@@ -8,6 +8,9 @@
   "sources": [
     "src/**/*.cs"
   ],
+  "test_sources": [
+    "tests/*.cs"
+  ],
   "depends": ["shell2d_base>=1", "interactive_base>=1", "effects_base>=1", "time_base>=1", "map_base>=1", "ui_base>=1"],
   "ui": [],
   "test_suites": [