fix artifacts, external deps and update SignalR

[analogrelay]

• Unreverts 952dbae68df4b0e49909d201e6e81df466b8316a which adds new packages to SignalR build
• Add SignalR to metapackage and add entries for new SignalR packages to artifacts.props
• Update SignalR submodule to remove use of private package System.Buffers.Primitives.

[natemcmaster]

Looks like you'll need @jbagga's changes too: #774

[ryanbrandenburg]

@jbagga merged, @natemcmaster he may as well not wait for appveyor since it's already broken without this anyway right?

[natemcmaster]

This needs to rebased on dev. As long as either Travis or AppVeyor passes,