Add several sanity checks

There are several conditions triggering errors or warnings due to missing sanity checks. Commit should fix the following conditions:

* Output is messed up if MySQL is not configured correctly -> Abort if no connection can be established
* Several constants are redefined because files get included multiple times -> use require_once instead of require
* If no auctions are present the script still tries to read items and fails -> do not show anything if no items are present
* Log parsing may fail if esniper crashed and returned an empty log file -> parse only if log is >0 byte
* Watchlist parsing may fail due to incorecct formatting -> not fixed but script will not throw errors for now
* setperms wants to set +x for esniper binary, however it is no longer bundeled
* use setperms to create a temporary folder