Merge pull request #78 from mgage/release/2.7

Potential fix for the "missing   css/images " error
Provide better solution to the numOfAttempts issue

 Insures that the number of attempts defined in the environment is correct.
 It is the sum of the number of incorrect attempts, the number of correct attempts
 and the number of ungraded attempts (which is 1 or 0 depending upon whether an
 answer has been submitted).
 The calculation is done in PG.pm
Merge branch 'release/2.7' of https://github.com/openwebwork/webwork2 into release/2.7