Long overdue rationalization of makefiles and scripts ...

Now, there is only one makefile and one script that does TeX compilation
in all cases. Moreover, all intelligence has been moved to shell-scripts
where its easier - and quicker - to make modifications

The changes here go hand-in-hand with the other changes in Rails and Java code
Defined our own environment - called explanation - for writing solutions

The new environment ensures that each question gets half-a-page
if nothing is specified. This is a better/safer solution than changing
the default in exam.cls itself

All new questions will get have the explanation environment only.
However, compile.sh has been edited to replace all solution
environments with the new explanation environment
[clean_tex]: Removes fullwidth environment and \insertQR also ...

The former has started showing problems - which I am too lazy to diagnose.
The latter is not needed as the newer \embedQR is inserted by
TeX callbacks anyway
No need for \begin{table} to enclose \tabular environment
Bringing back siunitx
Removing table environment during TeX cleaning ...

Like fullwidth, the table environment is also causing TeX to barf.
The following might be the issue - though I don't really understand it well

http://www.tex.ac.uk/cgi-bin/texfaq2html?label=extrabrace
Tweaking logic for toggling bottomLeftQR boolean
Re-written solution
Moved calculator within pkgs/
Merge pull request #606 from abhinavc/master

Single makefile and shell-script for all scenarios