Aggregation bar link drilldown doesn't wrap repo and file queries in ^...$

Created by: felixfbecker

When aggregating by repo and clicking a bar, the repo filter is not surrounded with ^``$. This means that a repo filter like github\.com/sourcegraph/sourcegraph will match a bunch of additional repositories that have sourcegraph- as a prefix.

The same happens for file: filters.

/cc @joelkw @felixfbecker @vovakulikov @unclejustin