lock access to userstocreate.txt from submit.php

[nanch]

writing to userstocreate.txt is not atomic and should be.

use a file lock (userstocreate.txt.lock) to guarantee that there is only one writer to the file at any given time.

reference: http://news.ycombinator.com/item?id=4561336

[nanch]

migrate createdusers.log and userstocreate.txt to sqlite3 and python scripts

this will add support for atomic operations, but will also add sqlite3 and python as dependencies

Database file: /usr/local/etc/tarbackup/db/tarbackup.db

createdusers.log will be migrated to table: Users

Users: Id, Name, Password, Email, Created

userstocreate.txt will be migrated to table: UsersToCreate

UsersToCreate: Id, Name, Password, Email, Created