Some smaller improvements on error logs/exceptions, ignores, file-checks, ...

[centic9]

A number of smaller adjustments:

• Add a .gitignore to ignore some of the files/directories created by grails applications
• Add some checks for things that we saw while starting to use Ice
• The null-check in Config.java is too late currently
• We saw some zero-length files in some cases, e.g. when the disk ran out of space before and you freed up space, Ice still wouldn't re-download the files

[cloudbees-pull-request-builder]

ice-pull-requests #61 SUCCESS This pull request looks good

[cloudbees-pull-request-builder]

ice-pull-requests #62 SUCCESS This pull request looks good