Added a panic recovery middleware after the logger so that we know what the query was that triggered a panic

[fkaleo]

No description provided.

[Dieterbe]

Great that this logs the entry we needed + fixes the metrics
but I don't like that it repeats the entire stacktrace, and in such an ugly way...

...
metrictank_1    | /home/dieter/go/src/github.com/grafana/metrictank/vendor/github.com/go-macaron/inject/inject.go:135 (0xab10d8)
metrictank_1    | /home/dieter/go/src/github.com/grafana/metrictank/vendor/gopkg.in/macaron.v1/context.go:121 (0xacbe48)
metrictank_1    | /home/dieter/go/src/github.com/grafana/metrictank/vendor/gopkg.in/macaron.v1/router.go:187 (0xaddb66)
metrictank_1    | /home/dieter/go/src/github.com/grafana/metrictank/vendor/gopkg.in/macaron.v1/router.go:294 (0xad7fcd)
metrictank_1    | /home/dieter/go/src/github.com/grafana/metrictank/vendor/gopkg.in/macaron.v1/macaron.go:220 (0xad0bea)
metrictank_1    | /usr/lib/go/src/net/http/server.go:2807 (0x7420e2)
metrictank_1    | /usr/lib/go/src/net/http/server.go:1895 (0x73db5b)
metrictank_1    | /usr/lib/go/src/runtime/asm_amd64.s:1373 (0x467100)
grafana_1       | t=2020-04-16T17:47:17+0000 lvl=eror msg="Request Completed" logger=context userId=1 orgId=1 uname=admin method=POST path=/api/datasources/proxy/2/render status=500 remote_addr=172.19.0.1 time_ms=3 size=6076 referer="http://localhost:3000/dashboard/new?panelId=2&edit&fullscreen&orgId=1&from=now-5m&to=now"
metrictank_1    | 2020-04-16 17:47:17.695 [INFO] ts=2020-04-16T17:47:17.695183308Z traceID=66f58767d7e167d8, sampled=true msg="POST /render?format=json&from=-5min&maxDataPoints=1870&meta=true&target=asPercent%28metrictank.stats.docker-env.default.tank.metrics_active.gauge32%2CconstantLine%28100%29%29&until=now (500) 2.598738ms" orgID=1 sourceIP="172.19.0.1, 172.19.0.1" error="%3Chtml%3E%0A%3Chead%3E%3Ctitle%3EPANIC:%20runtime%20error:%20integer%20divide%20by%20zero%3C%2Ftitle%3E%0A%3Cmeta%20charset=%22utf-8%22%20%2F%3E%0A%3Cstyle%20type=%22text%2Fcss%22%3E%0Ahtml%2C%20body%20%7B%0A%09font-family:%20%22Roboto%22%2C%20sans-serif%3B%0A%09color:%20%23333333%3B%0A%09background-color:%20%23ea5343%3B%0A%09margin:%200px%3B%0A%7D%0Ah1%20%7B%0A%09color:%20%23d04526%3B%0A%09background-color:%20%23ffffff%3B%0A%09padding:%2020px%3B%0A%09border-bottom:%201px%20dashed%20%232b3848%3B%0A%7D%0Apre%20%7B%0A%09margin:%2020px%3B%0A%09padding:%2020px%3B%0A%09border:%202px%20solid%20%232b3848%3B%0A%09background-color:%20%23ffffff%3B%0A%09white-space:%20pre-wrap%3B%20%20%20%20%20%20%20%2F%2A%20css-3%20%2A%2F%0A%09white-space:%20-moz-pre-wrap%3B%20%20%2....

[Dieterbe]

fix #1782