ENYO-368: Remove all instances of a property when removing styles before node is attached.

### Issue
When a control's style is removed before its node has been attached to DOM, only the first instance of the property is removed. This can cause issues in such cases as when a `FlyweightRepeater` is stamping out items, and we are modifying the style of a shared element.

### Fix
We add the `gi` flag to perform global, case insensitive matching for our regular expression when removing a style property, pre-attachment.

### Note
In terms of performance implications, this is a few percent slower: http://jsperf.com/regex-global-vs-no-global/2. If this is a concern, I have an alternate fix that patches the specific sample where this issue was originally raised: https://github.com/enyojs/layout/compare/ENYO-368-aarontam.

Enyo-DCO-1.1-Signed-off-by: Aaron Tam <aaron.tam@lge.com>