[WIP] addSiteLink and addNewSiteLink

Rename `addObject` to `addSiteLink` and `add` to `addNewSiteLink` as discussed in #109.

I'm not 100% sure if we all agree on that naming scheme, therefor the [WIP]. @JeroenDeDauw is fine with it according to #109. @brightbyte seems to be fine with it according to the (very short) discussion I had with him. I'm almost sure I'm fine with it.

Should be merged before releasing 1.0 and possible before releasing the 0.8 branch.