Add suggestions to some predicates

[rgehan]

If a token is provided, we could fetch the list of:

• All the repos the user has access to
• All the organizations the user has access to
• Maybe all the labels of these repos (might be too heavy, would need to be cached)
• Maybe all the users of these organizations (same as above)

This would allow adding suggestions to predicates such as:

• repo
• user
• involves
• commenter
• organization
• label
• etc