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.ts

@@ -930,6 +930,9 @@ export class InputHandler implements IInputHandler {
           this._terminal.viewport.syncScrollArea();
           this._terminal.showCursor();
           break;
+        case 2004: // bracketed paste mode (https://cirw.in/blog/bracketed-paste)
+          this._terminal.bracketedPasteMode = true;
+          break;
       }
     }
   }
@@ -1100,6 +1103,9 @@ export class InputHandler implements IInputHandler {
           this._terminal.viewport.syncScrollArea();
           this._terminal.showCursor();
           break;
+        case 2004: // bracketed paste mode (https://cirw.in/blog/bracketed-paste)
+          this._terminal.bracketedPasteMode = false;
+          break;
       }
     }
   }