Add 'TOPA notice type' filter to map view

[emkap01]

2 filters needed: TOPA: Notice Type, and TOPA: Notice Count

Per Issue #401, users will need the ability to filter the map view based on the type of TOPA notice covering each project (although not all projects will have TOPA notices). Since any given project can potentially be covered by multiple TOPA notices, we will also need a filter for the TOPA notice count per project.

TOPA: Notice Count - Users also want the ability to see which projects have more TOPA notices associated with them than others.

• add a calculated field to the project table with number of topa notices by joining to the topa table
• add calculated field to the filter API endpoint
• add a slider by adding it to dataChoices.js

TOPA: Notice Type - The TOPA table in our Postgres db includes the field notice_type, which indicates the specific nature of the potential change.

Since topa notices are one-to-many with projects, this will require an enhanced filtering methodology in util/filter.js. Need to address #500 before we're able to do this.