support collectd threshold states in dashboard CSS

[dch]

After this patch, pointing a tuned collectd install including thresholds will highlight threshold warnings and failures directly in the riemann dashboard.

Note this is not a "clean" change, as it includes adjustments to allow clean integration with collectd:

• Riemann uses ok|warning|critical to colour states in the dashboard.
• CollectD sends okay|warning|failure notifications via @pyr's write_riemann plugin, along with the original event.

Alternatively this could be patched on collectd side, or rewritten in riemann.config.

[pyr]

@dch, i'll submit a patch on collectd's side as well, thanks for the report

[aphyr]

Thanks dch, pyr! :)

[pyr]

just to let you know, there's collectd/collectd#271 waiting to be merged which will emit states the way riemann expects them, sorry about that!