Add ping support for retail

[drnoonien]

I don't really know what I'm doing, but figured this would be the easiest way to raise the feature-request. It seems to be working from what little testing I did, but someone more competent should take a look at it.

Docs for ping can be found here: https://warcraft.wiki.gg/wiki/Patch_10.1.7/API_changes#Ping_system

Random example implementation as seen in Grid2: https://github.com/michaelnpsp/Grid2/commit/905f3d1057ca69666513ae515f96e6aea522a871

[lemieszek]

clean and simple

first 3 are required, I am just not sure if Nevcairiel want the mixin or write the handlers himself thanks for the PR!

[adbir]

Any chance this gets in? Tested it locally and it works

[Nevcairiel]

I've added Ping support using the template instead, which seemed a lot easier