Add refresh to judgehosts page, sync all refresh times to 15sec
(except for scoreboard).
Prioritize single submission rejudgings.

The judge is typically interested in a quick result, while the
normal prioritization of submission according to team last judged
time would prevent that.
Add test for lib/relations.php before including it.
Clarify usage of checktestdata --generate and --preset options.
Add checktestdata command SET to set variable to a value.
Fix editing zip files which contain binaries.
Reduce duplicated code by merging {show,edit}_executable.php
Rename submit to save when editing executables.
Clean up code in show_executable.php.
Removing script suffix while downloading.
Fixed PHP notices.
Display load on judgehosts overview calculated over
last 10 minutes and since start of contest.
Set default time_factor for all languages to 1.
Fix debug message in case argv is not processed completely.
Do not wrap between problem shortname and balloon symbol.
Rename import-export-config.php to be more consistent with other pages.
Penalty time is not a required filed.
Highlighting of contest trumps alternating row colors.
Update clock with JS immediately, not only when the first second elapsed.

This avoids that the clock "jumps" to another timezone after the
first second in the case that server and client timezones differ.
Notify admin in menu if one or more judgehosts are down.

update_clarifications has been generalised into update_menu and
uses proper json. this also solves a duplicate query being issued
for the amount of unread clarifications and the ugly output when
update_clarifications somehow throws an error.