Merge pull request #169 from jabadia/jabadia-attachments

jabadia delete local attachments
see local files using createObjectURL()
need to: 
- revoke the URL when deleting the attachment
- update the inmediate pop-up URL
replace the default URL that is set by attachmentEditor with the local file URL
first step into refactoring attachmentsStore.js
now, all attachment URLs are correctly revoked
refactored reading of files into attachmentStore.js
much simpler and nice!
need to test with real attachment files now
this caused one test to fail
remember, attachments management is optional
check for blob url in the locally stored attachments