Added list endpoints for taskflows

[psavery]

Two different types of lists were added:

1. List taskflows for a given user.
2. List taskflows for all users.

Their endpoints are GET '/taskflows' and GET '/taskflows/all', respectively.

The "List taskflows for a given user" will use the current user if no user is provided.

I followed the example of the list endpoints in the girder "job" plugin while doing this. I also tested it and it seems to work fine.

Let me know if I should make any changes.

[psavery]

Looks like they removed requirements.txt from the root directory of girder...

[psavery]

I pushed an update here. Hopefully, the tests will pass. Let me know if I should change anything else.