Add user login command

[bgins]

Summary

Problem

Currently there is no way for a user to access their sites from a different computer then the one they originally created their account on.

Impact

Without this ability users won't be use their account from another computer or application. Users would also be unable to access their account at all if their original DID was lost.

Solution

Create a new command that allows the user to give all permissions to another DID.

Details

Currently the code for logging in the user written in Haskell. See more about this problem here.