Merge branch 'development' into scribing-qns
Refactor PDF to PNG conversion to a use a service object

Also generate PDF filename using SecureRandom and sanitize PDF filename
before using it as the output file basename.

References Coursemology/coursemology.org#277
Merge branch 'scribing-qns' of https://github.com/kxmbrian/coursemology.org into scribing-qns
Fix incorrect redirect and creation of empty question after uploading
PDF files.

file_save_success was out of scope when used previously. Use a new
variable png_success to indicate that PDF workflow was invoked. Short
circuit the if condition evaluation and thus prevent the creation of a
blank question when the PDF workflow works properly.

References Coursemology/coursemology.org#277
Only show canvas with attached pic when editing a scribing question.

Pull canvas code out to a partial and only invoke it when calling the
edit template. Pass a variable into the form partial so it knows whether
to invoke the canvas partial.

References Coursemology/coursemology.org#277.
Merge pull request #5 from fonglh/scribing-qns

Refactor PNG conversion code, fix redirect after PDF upload