fixes #16647 dojox.mobile.ProgressIndicator is not vertically centered.

Update common theme (`ProgressIndicator.less`, `ProgressIndicator-compat.less` and `ProgressIndicator-compat.css`) to use relative position in percentage instead of fixed px.

Potential side effect: application that benefit having `top: 180px` relative to a 0px height container would have to  add the ProgressIndicator as a child of `win.body()`. (win = `dojo/_base/window`).

See https://bugs.dojotoolkit.org/ticket/16647.