Added methods to get deployment specific rails / linode server paths

The paths are needed as we now plan to issue curl requests from
within the Makefiles upon re-compilation of a question. The requests
will update:
  1. the answer_key_span for a question (using pdfinfo)
  2. the number of unique codexes for a question (if any)
New method to return the exact PDF span for a question ...

This method calls pdfinfo - which is infinitely more reliable
than any algorthmic inference we could make.
Also, this method factors in whether there is a codex for this
question or not.
Abstracted code for find relative paths of folders within vault/
Get the exact answer key span using pdfinfo ...

And send the span back in a curl request so that the Question
object can be updated. Do this as part of question compilation.
Dotting i's and crossing t's for codex generation
Set an empty author if compiling in vault/

We need \setAuthor to set versions. But we need the header to be blank
so that the codices are narrow strips
Codex added
New environment - codex - defined ...

Absolutely the last thing written in question.tex - after \end{solution} or \end{parts}.
Merge pull request #702 from abhinavc/master

Makefiles, shell-scripts and .cls modified to support auto generation of codices