Support bracketed paste mode

- As described in https://cirw.in/blog/bracketed-paste
- Example support in vim:
  - https://github.com/ConradIrwin/vim-bracketed-paste/blob/master/plugin/bracketed-paste.vim
  - http://vimdoc.sourceforge.net/htmldoc/term.html#raw-terminal-mode
- Required for e.g. ipython, via python-prompt-toolkit:
  - https://github.com/ipython/ipython
  - https://github.com/jonathanslenders/python-prompt-toolkit

Repro:
- Run `ipython` (version 6.2.1)
- Copy multiple lines of text and paste into ipython prompt, e.g.
```py
print(1)
print(2)
print(3)
```
- Before: first line would paste and run, and subsequent lines are lost
- After: all lines paste into single prompt

src/InputHandler.test.ts

@@ -66,4 +66,18 @@ describe('InputHandler', () => {
       assert.equal(terminal.options['cursorBlink'], false);
     });
   });
+  describe('setMode', () => {
+    it('should toggle Terminal.bracketedPasteMode', () => {
+      let terminal = new MockInputHandlingTerminal();
+      terminal.prefix = '?';
+      terminal.bracketedPasteMode = false;
+      let inputHandler = new InputHandler(terminal);
+      // Set bracketed paste mode
+      inputHandler.setMode([2004]);
+      assert.equal(terminal.bracketedPasteMode, true);
+      // Reset bracketed paste mode
+      inputHandler.resetMode([2004]);
+      assert.equal(terminal.bracketedPasteMode, false);
+    });
+  });
 });