Adds a set of options to the essay question type which implement
the following new features:
-Adds an input format which accepts only file uploads, and no
inline text.
-Adds an option to make the inline text response optional when
attachments are enabled, so students can choose to upload
an essay file.
-Adds an option to make attachments required, so essays without
attachments will be marked incomplete.
The problem was with the non-UTF-8-safe way that a question name
was being constructed from the question text.
I have done a proper fix with methods in the base class to
carefully construct a question name that is reasonable, and
which will fit in the database column. Then I have changed all
importers to use the new methods.
I also remembered not to break the lesson in the process.
Using consants to refer to plugin names is crazy. The whole point of
plugins is that you can install more, hence the list of constants will
never be complete.
Sadly, this involves a small API change, but I don't believe anyone was
using the argument I had to remove (because we were sometimes passing a
wrong value, and there is not way to compute the right value at that
point in the code.)
Also sadly, the code to compute the context we are importing into is now
rather spaghetti-like, but it works.
