Migrate from Attachments to Files for storing logs

[jongpie]

Taken from the Spring '17 release notes, Salesforce has announced that "After Winter ’18, the Notes & Attachments related list will no longer have an Upload File button"

Nebula currently stores log files as attachments, so the code needs to be updated to use Files instead.
This could be done when doing issue #56 ("Incoporate the new Platform Events") to try to give logging as a whole some enhancements.