fix(templating): another fix for repeating panels and having old panels/scoped vars stuck after switching repeat variable, fixes #5795

fix(graphite): minor fix/improvement to graphite error handling when doing metric exploration in query editor, fixes #5778

* One of the homebrew folks first asked for a wrapper script to make launching grafana easier. Later I was asked to remove it and submit it upstream, so here it is.

* add instructions for installing grafana HEAD from git with homebrew back to the docs

feat(templating): fixed issue with template variables set to reload on dashboard load being issued multiple times, fixes #5637

Using these two values ties requests to a
particular query position within a panel, ensuring
that requests are canceled if:

- Duplicate requests with the same query are sent
- Requests from the same query position (but a
different query) are sent

The last point is important as it identifies
queries by a physical location in the dashboard
instead of with the query expression.  If a
different query from the same position in a panel
is sent, the previous request should be canceled.