Default spark Image skin shouldn't use Range base class

Steps to reproduce:
1. Look at the default spark Image skin (spark.skins.spark.ImageSkin), specifically the progress indicator:
...
<!--- Progress indicator skin part. -->
<s:Range id="progressIndicator" skinClass="spark.skins.spark.ImageLoadingSkin" verticalCenter="0" horizontalCenter="0" includeIn="loading" layoutDirection="ltr" />
...

2.
3.

Actual Results:

As pointed out in SDK-30700 the Range component is a base class and apparently we don't really recommend people use it in MXML. It works fine, but it does not have a default skin so you must specify a skinClass. Since we don't seem to want people using Range in MXML the SDK shouldn't do it either because we suggest that people copy/paste default skins and tweak them from there.

Expected Results:

After talking with Kevin we could do a couple things here:

• Make a new ImageProgress component that is a simple subclass of Range that has a default skin
• Replace Range with the spark ProgressBar when it is finished
• At the very least there should be a TODO/FIXME in the code to document and one day improve this unsuggested/hacky behavior

Workaround (if any):