The initial idea was to keep it separate since the unattached
links were also to be displayed distinctively from the metrics.
With the new design, unattached links are rendered in the same
list as metrics with attached links.
Therefore, we treat unattached metric links as an empty metric.
* Helps reduce garbage (MakeMetric() now takes a slice and there's a shorter version MakeSingletonMetric())
* Fixes bug computing Max (Min) in samples since using MakeMetric()
was causing a default Max/Min of zero.
* Simplifies code a bit
Also:
* Remove Gob encoder/decoder
* Stop using custom encoders/decoders for Timestamps (both ugorji and the Golang JSON codecs use nanosecond precision).
* Use idiomatic way to check for existence in metric.LastSample()
Squash of:
* Include plugins in the report
* show plugin list in the UI
* moving metric and metadata templates into the probe reports
* update js for prime -> priority
* added retry to plugin handshake
* added iowait plugin
* review feedback
* plugin documentation
