fix: properly break after metric is matched by a plugin

this was a regression introduced in the commit:
'deprecate the concept of multiple targets per metric'
deprecate the concept of multiple targets per metric.. continued

make structured metric plugins only return 1 match:
return the first match from target['match_object'], instead of
all matches. this is practically equivalent because (at least for
all plugins that come with graph-explorer) only have one match regex
per target.

this ensures in structured_metrics.list_metrics() we only have 1
proto2 metric per proto1 metric.
fix format of proto1->proto2 upgraded metrics

new style since elastic search, same as metrics from carbon-tagger
fix sys.path appends
remove old sql related function
easily toggleAble experimental highcharts plotting