Servo library support (#1343)

* ateempt at bringin servos

* basic plumbing

* avoid math map duplicate

* missing parts annontation

* pretify parts

* extend appcompat layer

* updated strings

* more compat layer

* annotations

* don't rely on webmidi

* updated pxt ref

* bump pxt

* adding whenUsed

* updated v1 readme

* more pins

* more pins

* compress the parts definition

* update common packages

libs/servo/pxt.json

@@ -0,0 +1,3 @@
+{
+    "additionalFilePath": "../../node_modules/pxt-common-packages/libs/servo"
+}