Support on disk GeoWebCache tilecaches

[bjornharrtell]

This PR provides a Source that can read tiles directly from a preseeded GeoWebCache cache dir that has been exposed on a webserver.

Adapted from @tschaub's experimental code for OpenLayers 2 here:
http://dev.openlayers.org/sandbox/tschaub/gwc/lib/OpenLayers/Layer/GeoWebCache.js

[ghost]

Added example data and made zeroPad private. Thanks for the suggestions @tsauerwein.

[ghost]

I think this is ready for review, but I cannot change the pull request title to remove [wip].

[elemoine]

Note that the build fails on Travis.

[bjornharrtell]

Fixed now.

[elemoine]

LGTM. Does anyone from Boundless interested in reviewing this? Are preseeded GWC caches common and actually used in practice? I have no opinion, just asking.

[bartvde]

I think this is useful

@elemoine so you have reviewed the code already? If so, I think we should merge this in?

[elemoine]

Please add a dot at end of line. We use punctuation elsewhere.

[elemoine]

@bartvde I added comments, but I think I have more.

[bartvde]

@elemoine cool TIA it wasn't clear to me if you had already reviewed (since you said LGTM)

[elemoine]

I had looked at it, but another look actually raised comments :-)

[bjornharrtell]

Thanks for the double review @elemoine :) Should be amended now.

[bjornharrtell]

Hang on, gjslint didn't like my @Private additions. I'll try to fix that and update.

[elemoine]

My last comment would be about support for multi-domain URLs, which other tile image sources support.

[bjornharrtell]

Looking at how other tiled sources works with URLs it might be possible to rewrite this PR to use ol.TileUrlFunction.createFromTemplate and friends and in the process get support for multi-domain URLs.

[elemoine]

Exactly.

[ahocevar]

Closing due to lack of activity. Also, the way we create tile urls has changed since. @bjornharrtell, please reopen if you are able/willing to continue working on this. And sorry for letting your valuable work go unnoticed for such a long time.