Fix user creation error and more, see description...

[joshuacant]

Hi, feel free to reject this if you're not interested.

Does the following:

• Fix user creation error
• Only creates db if needed, otherwise reuse existing
  • (a new filename is used to ensure a fresh db is created with a valid user)
• Prevent command output from writing to crash.log
• Reformat lua code to more closely match KOReader style

[kevinfowler]

I ran into the same issue with the password being less than 12 characters long for the "create user" command. This is on a Kobo Libra Colour. I fixed it by just setting the password from "koreader" to "koreader1234" in the main.lua and it worked. I was getting a "500 server error" when trying to login before that. Your PR would have fixed this.