Online repo for environments

[pennings-tamu]

All the available repos a user can import are stored inside this repo under environments-repo/. This was always just a temporary solution. The goal was to use a proper outside "env-store".

Plan:

1. create env-store that holds all the envs (elements can be stored as json objects, database format, etc)
2. make the JSON file describing the env required; right now, it's optional; aside from the name and description, it should also include the cluster the env is created for (later, we can add more fields, e.g., class of env).
3. update import window to retrieve envs from the env-store instead of the directory. Add a filter for cluster name later. Future features include ,add additional filters
4. after selecting, drona will import the env to the user's directory

For the env-store there are different options. Oneoption is the public GitHub repo where we retrieve it from. Also makes it easy to manage envs and for other parties to upload new envs. Alternatively, we host it somewhere else (e.g. on our clusters).