Add APM repo as a filter

[lkngtn]

Is your feature request related to a problem? Please describe.

Apps are published to different APM repos (eg open.aragonpm.eth, or at the top level aragonpm.eth) these repos have different processes in terms of publishing requirements and this is useful for people to understand and trust different apps. It would be helpful to be able to filter by APM repo.

Describe the solution you'd like
Add filters (like in the org tab) with the first (and only filter) being the APM repo.

Describe alternatives you've considered
Have not considered alternatives.

Additional context
This will help users leverage apiary for application discovery, and may be loosely related to the larger initiative described in #79