Add password-based login to Admin page

[taoeffect]

Requirements:

• Passwords stored on disk using either bcrypt or scrypt (latter preferred)
• Password itself never sent over the wire
• Ability to change password
• On first load of admin interface, set the password. ABSOLUTELY NO DEFAULT PASSWORDS OF ANY SORT!! Grrr!! 😾

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[taoeffect]

@wemeetagain I'll work on this with you. I think a good plan of action is to:

1. Work on the admin branch (maybe rebase it again off of master, if necessary, depending on what else we decide to do first)
2. You can focus on the actual GUI aspect of this and storing of the password to disk
3. I'll implement the password hashing part (ensuring proper bcrypt/scrypt usage)