Update "Back To Samples" button

[teckliew]

Right now we have a "Back to Samples" button that is hidden, transparent, and hard to read:

Use IconButton instead and have it shown at all times in the corner where the closex in Panels is so that it isn't hard to find.

[Djspaceg]

Well that looks really nice!

[Djspaceg]

Is it really important to specify the colors here? Could we instead use one of the built-in features of the button to get a similar compatible effect?
I mention because I fear that we have or will have a skin or skinVariant changing sample, which would make this direct assignment look out of place, in addition to the next Theme library using a specific tone of gray for the background rather than black.

[teckliew]

Added in MoonstoneDecorator to take care of styling. Also cleaned up the styles a little bit.

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