Change venvFolders to no longer be anchored to the user's home directory

[brettcannon]

We discovered during our bug bash that venvFolders exists but isn't documented. Either we leave it, document it, and potentially not make (at least) our pyenv support depend on .pyenv being in it, or we remove the setting and use the documented functionality of pyenv directly.

[brettcannon]

1. Make pyenv and direnv support not rely on venvFolders
2. Create venvPaths which is an array of directories which contain virtual environments
3. Deprecate venvFolders and venvPath
4. Make sure environments list gets updated when settings change

[brettcannon]

#2142 is a motivator for venvPaths available.

[brettcannon]

We may want to consider skipping step 2 and modifying step 3 to only worry about venvPath as the naming of venvFolders makes a little bit more sense in isolation then venvPaths.