Add https support for CartoDB

[ilyankou]

Fix #189

The idea is to have two properties, url and url2 for https and http protocols respectively, for those basemaps whose links are different for the two protocols (when // does not do the job).

[brunob]

This PR make me think that we may simply use https every time a provider allow it (and ditch http for these cases). This would simplify our code and it's not a problem or am i missing a point ?

Now that SSL is encouraged for everyone and doesn’t have performance concerns, this technique is now an anti-pattern. If the asset you need is available on SSL, then always use the https:// asset.

https://www.paulirish.com/2010/the-protocol-relative-url/

Any thoughts about it @jieter ?

[jieter]

Makes sense. Also helps for those working locally over the file:/// protocol.

[brunob]

closed in favor of #258