Fix of mobile virtual keyboard fix

Fix a few issues of PL #9.

## Changes

1. Detect user-agent before executing mobile-only code. This should keep desktop version's behavior unchanged.
2. Move the hidden input along with the cursor to get the correct scrolling behaviors.
3. Update jQuery to version v1.11.1

## Test Browsers

* Desktop (Windows 7 x64)
  - Chrome 35.0.1916.153
  - Firefox 29.0.1
* Mobile (iPad2 iOS7)
  - Safari
  - Chrome

## Known Issues (not bugs)

1. Input's caret won't hide on certain mobile browsers like mobile Safari. There's nothing much can be done since it's browser feature and out of CSS's reach.
2. Certain mobile browsers, like mobile Safari, will ignore most `focus()` calls to get better performance. Input can be only focused from a mouse event handler. This causes the input to lose focus, which cases virtual keyboard to disappears, every time a command is entered.