Reenables & improves city filter

[psdcode]

This PR rebuilds and reenables the city filter. Resolves issues https://github.com/ajah/sks-interface/issues/49 and https://github.com/ajah/sks-interface/issues/34

• A maximum of 5 cities can be filtered for
• Each city can be a max of 30 characters
• Adding a city automatically updates search results
• Using 'Enter' key when focused on the field adds the city
• Cities displayed with pills below the text field, each with a remove button
• Duplicate entries are ignored

Other fixes:

• When redirected to homepage from a bad url, clears address bar to the homepage pathname /

To confirm with @brittwitham :

• The /count route currently does not seem to take the params other than q and operator, so count results returned do not take any other filter into account.
• Backend seems to use AND on all words within a city search term: Adding "New York" brings results for "North York" and "New Jersey". Do we want this?

Time spent: 2.5hrs

[brittwitham]

@psdcode the fixes look great, functionality is as expected.

You make some good points about the /count endpoint and adding phrases to the city search - I'll have Gustavo add these as issues. Thanks!

[psdcode]

@psdcode the fixes look great, functionality is as expected.

You make some good points about the /count endpoint and adding phrases to the city search - I'll have Gustavo add these as issues. Thanks!

@brittwitham Sounds good! btw, in the original comment I think I meant OR instead of AND: "Backend seems to use OR on all words within a city search term"