Loading dialog

[orangemug]

When opening a style from the network, for example clicking one of the 'Gallery Styles'. If you're on a slow network nothing will happen for a period of time while the request/response completes. This isn't a very good user experience. Also if you close the model once the request completes it will currently still load the style.

Suggested solution: When you open a style from the network open a blocking modal that says, something like

Loading style: [URL].json

With a single button cancel

[orangemug]

Almost complete on branch master...orangemug:feature/loading-modal.

Just requires a tidy of the styling.