Use hexdump of zipfile instead of LOAD_FILE.

LOAD_FILE does have a couple of restrictions (e.g. only loads files
from server not from client). LOAD DATA LOCAL does not work with BLOB
columns. So, generate and load hexdumps manually.
Get rid of intermediate .in files for executables.
Reduce duplicated code while generating sql for executable files.
Create judgehost user with appropriate credentials and rights.

Generate restapi.secret along with dbpassword.secret. Add judgehost
user with appropriate credentials/rights to the database.
Use teamid instead of 'domjudge' when resubmitting a contestants code.
Need zip for zipping
htpasswd not used anymore
Fix commit 47c308690.
Files from executable can now be changed via webinterface.

TODO: Refactor/extract common code.
Fix compiler warning about redefining _XOPEN_SOURCE.