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/Terminal.ts

@@ -132,6 +132,7 @@ export class Terminal extends EventEmitter implements ITerminal, IInputHandlingT
   public originMode: boolean;
   public insertMode: boolean;
   public wraparoundMode: boolean; // defaults: xterm - true, vt100 - false
+  public bracketedPasteMode: boolean;
 
   // charset
   // The current charset
@@ -260,6 +261,7 @@ export class Terminal extends EventEmitter implements ITerminal, IInputHandlingT
     this.originMode = false;
     this.insertMode = false;
     this.wraparoundMode = true; // defaults: xterm - true, vt100 - false
+    this.bracketedPasteMode = false;
 
     // charset
     this.charset = null;