Feature/21: Geolocation map view

[aPruner]

NOTE: This PR is a WIP (Work in Progress) - DO NOT MERGE YET!

DONE:

• Created a MapView component that shows discussions (via the DiscussionPin and DiscussionPinTooltip components) on a Google Map (via Google Maps JS API and GoogleMapReact npm package) based on the location of the original poster's browser when the discussion was posted
• Added config/credentials.js to the .gitignore, added a blueprint called config/credentials-outline.js so that users can create their own local version of config/credentials.js to throw API keys and such into that don't get committed - docs on this to come (.env might be a better solution, but this was necessary for me to get the MAP_KEY variable working)
• Move the discussion button (remove the sidebar) in ForumFeed so that the MapView displays properly
• For some reason, the geoLocation wasn't actually being written to the Discussion model. Make appropriate backend API changes to do this
• Move react-geocode and navigator.geolocation geolocation-API related code into a re-usable Utils/geolocation.js file. We should expand this Utils library to include any utility-related functions that shouldn't exist inside component files. Examples of this might be regex validation, sorting, string manipulation, math, etc
• Concatenate PinnedDiscussions and Discussions arrays so that DiscussionPins on the map are created for both pinned and unpinned discussions (this is the result of a design flaw, there shouldn't be separate arrays for these in the first place)
• Pre-center the map based on user's location
• "Time since creation" label on DiscussionPin (Map Markers)
• Remove map from newDiscussion page
• Add a map on the singleDiscussion page
• Keep address input field visible on newDiscussion page all the time
• Clean up the code (remove console.logs, move code into utilities library where necessary, fix code-style stuff like spacing, comment grammar, etc)
• Add a map toggle (maybe, might create separate issue for this) - (Create separate issue)
• Colour-fade for DiscussionPins (Create separate issue)
• Determine and implement mobile behaviour for the feature (Don't show the map) (Create separate issue)
• Create ENV var for defaultCenter of the map (SF for demo)

STILL TODO:

• remove TODOs, general pre-merge clean up
• final testing and demo-prep

[aPruner]

Will update this PR with screenshots of the new UX elements/workflows

[aPruner]

@PimDeWitte new solution (as agreed upon in slack) for the default map centering is to just add 2 new env vars to config/credentials called MAP_CENTER_DEFAULT_LATITUDE and MAP_CENTER_DEFAULT_LONGITUDE