Implement hierarchy browser

[hannesgassert]

For countries for which we have a good tree structure being able to browse that tree in the UI would be very helpful.

Requirements:

• Go from a public body to its parent body (done)
• See a list of child bodies per public body
• Present overview per jurisdiction in tree / forrest form

[rufuspollock]

+1

[augusto-herrmann]

+1 That would be helpful. We do have hierarchy data available for Brazil's federal government.

[augusto-herrmann]

I'm interpreting this issue as the UI part of the data we are discussing about collecting in #61.

We also need to be mindful of performance issues here, as the full structure of the Brazilian federal government has over 73k entries, as can be seen here, with csv files over 124 MB.