Adding paging to "Your recent attempts" tab (#40)

on challenge page.
Merge remote-tracking branch 'upstream/master'
Fixing pep8 warnings.
Revising new_challenge.html to comply with ndb and new challenge model entity .
Revising new_challenge.html to comply with ndb and new challenge model entity .
Revising new_challenge.html to comply with ndb and new challenge model entity .
Revising new_challenge.html to comply with ndb and new challenge model entity .
Revising new_challenge.html to comply with ndb and new challenge model entity .
Reacting to code review, part 1:

various small edits.
Reacting to code review - adjusting stack

for recent attempts paging
Reacting to code review for #40 - adding AJAX

when "Your recent attempts" tab gets loaded.

Solves #117 as well.
Merge remote-tracking branch 'upstream/master'
Reacting to code review on #40 - minor changes.
Merge pull request #133 from mahdykhayyamian/master

Move back the name of the challenge from second column to the first column (column left) (issue #133)
Merge remote-tracking branch 'upstream/master'

Conflicts:
	src/templates/solve_a_challenge.html
Merge pull request #129 from egor83/master

Added paging to "Your recent submissions" tab (issue #40)
Part of #102 - buttons fix.

"Next"/"previous" buttons did not work.
Fixes #118 (Exception when

clicking "Solutions without reviews" on local build)
Adjustments according to pep8 (part of #118).
Merge pull request #138 from egor83/master

Further fix to #102