Add Change Password menu option

[burtonr]

Add a new dialog that allow users to set a new password for themselves.
If the user is an admin, also allow the ability to change a different user's password.

The dialog should have at least 2 text inputs:

• Current Password
• New Password

If the user is an admin, and they are changing the password for a different user, the fields should be:

• Username to change
• New Password

An admin will use this to set a new password for a different user who has forgotten their password, or had their password reset.

The request should POST to the API endpoint defined in #28