Extracted keycode constants from TermKeyListener
Added create and switch window/tab keyboard shortcuts

Switch forward with Ctrl+Tab, back with Ctrl+Shift+Tab
Create new with Ctrl+Shift+N
Added paste from clipboard shortcut (Ctrl+Shift+V)
Stop keyboard shortcuts breaking back key interceptor.

You can only have one key listener on a view,
see comments on pull #235.
Merge branch 'keyboard-shortcuts' of git://github.com/splondike/Android-Terminal-Emulator into splondike-keyboard-shortcuts
Add user preference for keyboard shortcuts.

Defaults to "on", but can be turned off for people who don't want the
shortcuts.
Guard against an empty clipboard.