Implement basic execution system and UI

This is a rather large commit that includes all of the following:
- React UI with code editor, runtime renderer and input-output panes
- Language providers for a sample language and Brainfuck
- Implementation of code execution in a web worker
- All-at-once unabortable execution of program fully functional

styles/editor.css

@@ -0,0 +1,12 @@
+.code-highlight {
+  background-color: #ffff0077;
+}
+
+.breakpoint-glyph {
+  box-sizing: border-box;
+  padding: 4%;
+  border-radius: 50%;
+  margin-left: 10px;
+  background-color: #ff5555;
+  background-clip: content-box;
+}