Ask before dropping database.
Add functions escaping strings for LaTeX.
Implement PrintingService.
Add printing frontend to CWS.
Use C++11 by default to compile C++ submissions.
Add documentation on programming languages details.
Fix cms.conf style
Merge pull request #332 from lucach/upstream

Fix cms.conf style
Allow Printing and Proxy service not to be present in cms.conf.

Both are required only in specific situation: when printing is enabled
and when there are external rankings, hence it makes sense to skip
them from the configuration if these features are not enabled.
Added logging explanation to two exceptions.

First is "wrong connection string", second is "service not specified
in conf". First still has several occurrence - we fixed only the case
in which the service accepts a contest id.

I introduced a new exception, ConfigError, which is supposed to be
used for critical configuration problems, and is catched only in the
scripts' main.
ES: refactor Job generation in search_jobs_not_done().

Create methods to decide what must happen to a Submission or to
a UserTest. The intent is to move all the similar logic in these
methods.
ES: add "submission_" prefix to some methods for consistency.
ES: finish refactoring Job generation.

All Job creation is factored through submission_get_jobs() and
user_test_get_jobs().

Also, fix some logging and reimplement lowered priority for Jobs
that have already failed.