Move createDefaultEditingStyles() to ol.style

[probins]

Fixes #2440. I think this is all that's needed.

[probins]

I got this to compile by copying what was done in #2394: make everything require ol.style.Style. But this surely isn't correct. ISTM style/style.js should be providing either ol.style as a namespace for the static functions, or the functions themselves, such as ol.style.StyleFunction.

[elemoine]

@probins based on your last comment I am not sure this PR is ready for review or not. Could you please clarify things?

[probins]

it's ready for review, and should work as #2394 does. But there's a broader issue of what style/style.js should be providing (goog.provide). That's a separate issue though.

[elemoine]

It looks good to me. @tonio, do you agree with this patch as well?

[tonio]

+1, thanks!