MicroBit extension, Scratch Link first draft. (#1230)

* First microbit gui tests

* Fixed JSONRPC inheritance.  Renamed ScratchBLE/ScratchBT files.  Removed ScratchBT test code from Microbit extension.  Renamed addLine to log.

* Fixed log comments.  Removed addLine from Microbit.

* Adding auto-connect to Microbit at extension loading.  Adding hack for displayText block to Scratch-Link.

* Resolved merge conflicts and brought in latest microbit extension example code.

* Updated microbit write tests for displayText and displaySymbol blocks.  Some linting.

* Some linting and adding of BLE Characteristic consts.

* Linting fixes.

* Moving micro:bit device connection code all to the MicroBit class, decoupling Scratch3MicroBitBlocks from connection code.

* Removing old disconenct handlers from MicroBit class.  Moved service into new BLEUUID data structure.

* Renamed _write to _send.  Moved all BLE encoding concerns to the _send method.

* Using the util log.  Some linting.

* Added _read method to MicroBit class.  Renamed _send to _write.

* Some linting and formatting comments.

* First pass at peripheral chooser pattern for ScratchBLE.

* Testing characteristicDidChange events, and some changes to ScratchBLE on ready events.

* Refactoring work on PeripheralChooser and ScratchBLE.

* Some variable renaming and method signature stubs.

* Peripheral chooser method signatures.

* Moved base64 encoding/decoding to util.  Some method signature formatting.

* Adding test stubs for new util and io classes.

* Adding test stub for MicroBit extension.

* Clean up for PR.

* Clean up for PR.

* Final cleanup for PR.

* Removed logging to console.

* Adding 'btoa' and 'atob' node modules and using them in Base64Util.

test/unit/util_jsonrpc-web-socket.js

@@ -0,0 +1,10 @@
+const test = require('tap').test;
+// const JSONRPCWebSocket = require('../../src/util/jsonrpc-web-socket');
+
+test('constructor', t => {
+    t.end();
+});
+
+test('dispose', t => {
+    t.end();
+});