General Palette improvements

Improve Palette in order not to allow insert elements from Palette to the wrong places.

1. Insert elements from Palette to the Editor by setting text cursor or selecting text in the Editor then pressing on Palette Item

Before Insertion	After Insertion

2. Insert elements from Palette to the Editor by dragging elements from Palette and dropping them to the Editor

A short video: http://www.screenr.com/207N