updating BatchTester to read Problem/TestCases from JSON

Also, got rid of ProblemReader, ImportProblem class, and
corresponding perl script; we haven't needed them for a
long time, since problems can be authored using the web
interface.
added an admin servlet to export exercise data as JSON

We check to ensure that the authenticated user is a course
instructor, the same as we do with the Problems servlet.
ignore .fifo and .pid files
started work on front-end for batch mode testing
added code to BatchMain to actually test submission (untested)

Made the Builder2.testSubmission method static and public
to enable this.
add model classes JSON jarfile to classpath
fix BatchMain (need to actually read the program text)
write a "failure report" with test output of failing submissions

this is sent to System.err so it can be captured separately
from the results.
increase problem description size from 8192 to 16384
Merge pull request #44 from daveho/master

batch testing, increase problem description size