Integrate PouchDB

[midsorbet]

To test this PR, please make sure to create a database called "test" and add "pouchIndex": "courses" to the documents in the courses database. (related to #48)

What Works?

• Authentication (Sign up, login)
• Courses module (only the courses services use pouch)

[midsorbet]

So, I added a check for this.course because it's null sometimes and gives an error when accessing the id.

[midsorbet]

For example, if you directly go to the step view page then BehaviorSubject is null and throws an error

[paulbert]

Ok here are some thoughts on this:

• I think we should not start with courses on this. This is actively in development and changing weekly, making the conflicts pile up quickly. I think feedback would be best.
• Before doing that, maybe let's just add in the PouchDB service into the codebase rather than try to integrate it fully into a section of the app. I know that has its own challenges, but there's so much changing here that it'll be easier to progress with a small change adding PouchDB
• The folder structure is adding an unnecessary layer (shared/services) when I think we should just have the couch and pouch services in a shared/database folder or even just a database folder.
• It's also easier to follow the changes if each commit isn't so specific (a few that I looked at were one line changes). We don't want to get too broad, but something in the middle would improve this.
• Thinking about it more, I think we need have separate PRs for adding interfaces. This will also help to reduce the size of this PR and get it moving faster.

[midsorbet]

Thanks for the feedback @paulbert. Closing in favor of #1355