Improves compatibility with xampp environments
Adds div container for better styling possibilities
Retrieves mime types by PHP methods to improve compatiblity to xampp environments
Sends errors in case of exceptions to the frontend
Displays errors if upload fails
Fixes media item initialization for new items
Revert "Adds div container for better styling possibilities"

This reverts commit 5b0379b98f1d5b4d11118b6dc37c4f2f36d99423.
Merge pull request #578 from nsendetzky/2014-04-06_upload

Improves compatibility with Windows XAMPP environments and displays errors if upload in admin interface fails