Added some minor changes to the excel exporter to reduce the number of exceptions that get thrown.
For ExplanationBuilder, made the renderGradingView() function display the lastAcceptedText for an idea if it does not have the idea basket to retrieve the idea text.
Fixed a bug where a CRater step would not display the previous student work in the greyed out textarea if the student left the step and came back.
Merge branch 'master' of https://github.com/WISE-Community/WISE-VLE