Add wrapX support

[StevenHeinrich]

Allows the wrapX property to be passed into the source. It has only been applied to sources that accept this property based on the OL3 docs. The pass-through property defaults to true, as it is in OL3.

This PR is very similar to #198. The exceptions being lack of ternary operator and only applying the property to sources that have support for it (to avoid confusion and properly match the OL3 docs). Sorry for the repeat PR. But, seeing that #198 was almost a year old and is listed as having merge conflicts... I just chose the simpler path forward.

[juristr]

Thanks a lot for this PR. Could you please rebase it to resolve the conflicts with the master branch? Then I'll merge it in immediately.

[StevenHeinrich]

Conflicts resolved 👍

[juristr]

Awesome, thx! Merged 👌

[thmitchell]

There is a bug.

wrapX: source.wrapX || true

The use of short-circuit evaluation for the wrapX property will always resolve to true when the possible values are undefined, false, or true.

// wrapX evaluates to true for all of these:
wrapX: undefined || true
wrapX: false || true
wrapX: true || true

Given that... the following seems more appropriate (this actually exists in the Openlayers implementation):

wrapX: options.wrapX !== undefined ? options.wrapX : true

Final thought... why not just let the Openlayers implementation handle the default values if wrapX is undefined? From my brief observations, most of the ol.source.* implementations have default definitions for the wrapX option.

https://github.com/openlayers/ol3/blob/v3.16.0/src/ol/source/xyzsource.js (line 55)