Merge pull request #3 from sethsnel/master

Minor bug fix for mapping process
Minor cleanup of unnecessary code
Fix for an issue with excel sheets containing emtpy sheets

Instead of returning the sheet count to the client now the controller
returns a list with indexes of correct and usable sheets.
New feature: User is informed about loss of data when going back to the mapping page.

I override the onclick event of the previous element on page 3, now it
informs the users about the loss of applied changes. The user can than
choose whether to continue or not.
version up and fixed the version of release plugin
removed log action
Merge branch 'master' of https://github.com/sethsnel/GDTImporter