Display current review in "other sub-s" (#143)

If current user has a review for a submission, display its content in a
review form and disable that form.

Fixes #143
Fixing pep8 warnings.
Reduced the amount of duplicated code

part of #143.
Merge remote-tracking branch 'upstream/master' into own_review
Reacting to code review (#143)
Showing other people's reviews

if thissubmission was already reviewed by the current user.

Part of #143.
Merge remote-tracking branch 'upstream/master' into own_review
Typo when settings a button class.
Reacting to code review-2 (#143).
Merge remote-tracking branch 'upstream/master' into own_review
Moving JS code from inside HTML

to a common onLoad handler for this page.
Merge remote-tracking branch 'upstream/master' into own_review

Conflicts:
	src/static/jeeqs.css
	src/templates/review_a_challenge.html
Merge pull request #153 from egor83/own_review

Showing existing reviews (fixes #143)