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/Interfaces.ts

@@ -48,6 +48,7 @@ export interface ITerminal extends ILinkifierAccessor, IBufferAccessor, IElement
   buffers: IBufferSet;
   isFocused: boolean;
   mouseHelper: IMouseHelper;
+  bracketedPasteMode: boolean;
 
   /**
    * Emit the 'data' event and populate the given data.
@@ -82,6 +83,7 @@ export interface IInputHandlingTerminal extends IEventEmitter {
   originMode: boolean;
   insertMode: boolean;
   wraparoundMode: boolean;
+  bracketedPasteMode: boolean;
   defAttr: number;
   curAttr: number;
   prefix: string;