Drag the <g>
element(parentNode), rather than the rect. This, then will include the text in the drag/drop event.
e.g.
<g id='Propositions'>
<rect id='Proposition1' onmousemove=dragMe(evt) x='50' y='50' width='100' height='30' style='fill:#8FBC8F; '/>
<text pointer-events=all x="55" y="72" font-family="Verdana" font-size="14" fill="black" > Proposition1</text>
</g>
function dragMe(evt)
{
myG=evt.target.parentNode
myG.setAttribute("transform", "translate("+transX+" "+transY+")")
}