add clipboard cleared toast

[codokie]

Now that #752 and #679 have been merged, I think it would be a good idea to show a toast as an indication that the "clear clipboard" toolbar key has been pressed.

[codokie]

FYI the fake toast visibility is not set to GONE by the view's handler if the keyboard is hidden before the message is handled.
Consider adding the following block to KeyboardSwitcher.hideWIndow()

if (mFakeToastView.getVisibility() == View.VISIBLE) {
    if (mFakeToastView.getHandler() != null)
        mFakeToastView.getHandler().removeCallbacksAndMessages(null);
    mFakeToastView.setVisibility(View.GONE);
}