implement database management tools

[nadako]

we need to develop some management tools for haxelib db so we can easily do support tasks, like lib/version removal, password reset, etc.

[nadako]

(i'm talking about tools for us to use, so we don't have to work with SQL directly, not haxelib end-users)

[ibilon]

After #342 I'm guessing there's no tool for library removal? Should also do one to check the integrity of the DB.

Note: we'll need to use these tools to clean the DB of old broken references.