Make tsconfig as strict as possible

This also makes it explicit which exceptions from full strictness that we rely on:
- noImplicitThis: Mostly in backbone patch
- strictPropertyInitialization: a bunch of properties initialized during backbone init calls is not covered correctly for this strict check
- strictFunctionTypes: The ISerializer interface makes all the arguments optional to allow simpler definitions (`deserializer: (value: any): unknown  => { ... }`). However, this does cause `unpack_models` to be typed

Author: vidartf

tsconfigbase.json

@@ -15,7 +15,10 @@
     "noUnusedLocals": true,
     "preserveWatchOutput": true,
     "resolveJsonModule": true,
-    "strictNullChecks": true,
+    "strict": true,
+    "noImplicitThis": false,
+    "strictPropertyInitialization": false,
+    "strictFunctionTypes": false,
     "target": "es2017"
   }
 }