Refactors search mechanics: Part 1

[psdcode]

Part one of a two part search mechanics refactor. In this PR:

• Refactors to move away from using search reactcontext for state handling, and towards the address bar as the single source of truth of search state
• Resolves https://github.com/ajah/sks-interface/issues/30
• Adds ability to choose the doc type filter via radio button menu for every search call (before some were always hardcoded to eg, search both activities and orgs)
  • This partly resolves https://github.com/ajah/sks-interface/issues/32 and https://github.com/ajah/sks-interface/issues/4
  • Removes unnecessary 'Update' filters button, since as per Gustavo, search should update automatically
• Fixes issue/discrepancy with Enter key vs clicking 'Search'

To come in part two early next week:

• add support for remaining existing filters (municipality, location, etc)
• add support for multiple (previously entered) keywords, as indicated by little tiles above search box
• move all axios api calls into api service file
• resolve a few other current issues (eg https://github.com/ajah/sks-interface/issues/38)

Note: a lot of the old code is still left commented out for reference