Use shortid.MustGenerate() instead of shortid.Generate(). Instead
of returning errors it will panic.

#7883

Introduces new url in api /dashboards/<uid> for fetching dashboard by unique id
Leave the old dashboard by slug url /dashboards/db/<slug> for backward
compatibility and for supporting fallback
WIP for #7883

Make the max length of uid longer in case we want to change it later
#7883

fix: InfluxDB Query Editor and selecting template variable in where clause caused issue, fixes #10402, fixes #10663

This reverts commit 475febd0.

* go1.9.3:
  tech: upgrade to golang 1.9.3