Element-web: Support for incoming webhooks

I'm not sure what the intended scope of the issue is, but I have a bridge for this: https://github.com/turt2live/matrix-appservice-webhooks

Newbie here. Tried to see how to set up github event notifications in a Matrix room similar to the way Gitter has it, and the only option is to allow the official Github bot to access everything at the admin level... this is by far not acceptable. We need a webhooks-based way of receiving notifications without asking for any access to Github at all.

@kvark riot is just a matrix client, you might want to look at go-neb or Travis' bridge above. Riot doesn't run whilst your browser isn't open so can't do things like webhooks