Improvements to the vanilla gatom editing abilities
Adds shift+up/down and up/down while selected to change number values only. Adds shift+click that allows on the text gatom to append to the previous text. Adds shift+backspace on the text gatom to delete all text (e.g. when in append mode). Adds ability to dynamically switch shift+click vs click (inc/dec by 1 or 0.01, respectively), while dragging the mouse.