Visualize Mapeo alert data on alertsDashboard

[rudokemper]

Closes #47.

Goal

This PR adds a comprehensive workflow to add Mapeo data to the alerts API and dashboard, and have all of the same behaviors as alerts (e.g. select a feature, change the color when selected, view in sidebar, download CSV/GeoJSON).

Screenshots

Can also explore here: https://bcm-views.guardianconnector.net/alerts/fake_alerts

What I changed

• The app now takes two new env vars (MAPEO_TABLE and MAPEO_CATEGORY_IDS) for an alerts view in NUXT_ENV_VIEWS_CONFIG.
• If set, the /alerts API will pull data from the MAPEO_TABLE var and filter only the MAPEO_CATEGORY_IDS - the idea here is that only specific categoryIds (e.g. those related to threats) from a Mapeo dataset should be shown on the map.
• AlertsDashboard receives this data from the API response as a prop, and using a new function addMapeoData, adds it to the map.
  • For clarity, addDataToMap and data were renamed to addAlertsData and alertsData, respectively.
  • For mouseovers, I noticed that hovering from one feature to another was resetting the cursor, so I added a featuresUnderCursor helper variable to store the number of features under the cursor. Now, the cursor only resets when that var is equal to 0, resolving the issue.
  • Introduce isAlert variable based on "Alert ID" field to differentiate alerts from Mapeo data, and use that to conditionally show/hide Media for each.
• Some small changes to components like Download, Feature, Map, mapFunctions (related to Legend) to get Mapeo data to work for the respective tasks in each component and/or look nicer.
• In Features, conditionally render a field data_source as a header. (For now, I just assume that it exists in the database table; would like to think through if this possible to introduce in frizzle.)
• I introduced some timestamp rewrites in transformData to render the created and modified fields as legible dates in the sidebar.
• In mapFunctions, I introduced new function prepareCoordinatesForSelectedFeature to rewrite a Mapeo [long,lat] coordinate to show as lat, long in the sidebar instead (e.g. for usage in Google Maps).
• The default point color was changed to blue to disambiguate them from orange alerts.

What I'm not doing here

• Identifying Mapeo vs. Alert data deterministically, which ideally should come from the database (e.g. maybe frizzle). Will file an issue for this later.
• Allowing the Mapeo data color to be set (I want to consider the best approach for this in later work).
• Filtering the Mapeo data e.g. by date.