Don't cache download responses

* Don't cache download responses in Amazon S3
* Remove AWS-SDK
Move login data to master DB

* move password field to master.users
* disable login with e-mail address
* disable md5 hashed passwords
* no need to update username, since it is no longer stored in two different places
No login via session cookie
All user accounts are only in master DB

* Do not add users from WWW DB
* All users are valid
Move user privacy settings to master DB
Only check personal quota
Remove unused DB classes
always use $_SERVER['REMOTE_ADDR'], even if it contains a private ip

this fixes an error if only private IPs are used
Add script to setup a minimal database
Add script to add new users
Add init-scripts to start zotero processors
prepare to update S3Lib.inc.php
add new upstream version of S3Lib.inc.php
reapply changes to new version of S3Lib.inc.php
getAuthenticatedURL: Use self::$endpoint instead of s3.amazonaws.com
S3Lib: always use path-style access
make the S3 endpoint configurable