Grey out layers in the toc if not visible due to scale

[umbe1987]

According to the official OGC WMS 1.3.0 specification:

The <MinScaleDenominator> and <MaxScaleDenominator> elements define the range of scales for which it is appropriate to generate a map of a Layer.

It would be nice to grey out layers in the toc if layers are not visible due to scale.
Use this to get current scale with OL and compare it with WMS capabilities.

[umbe1987]

Implemented as of df646eb. At present, seems to work fine for desktop monitors but not for smaler devices (i.e. smartphones).

The symptom: layers get greyed out in the ToC although they're still visible in the view.
For possible solution, see this link and try to make adjustments in https://github.com/umbe1987/shire/blob/master/js/get_scale.js.