Upgrade logging to be compatible with CocoaLumberjack 2.0.0-beta4

Upgrade CDT Logging macros to use the new updated logging macros
from CocoaLumberjack 2.0.0-beta4. This will mean that it will not work
with versions below 2.0.0-beta4, thus also pin podfile to
CocoaLumberjack version 2.0.0-beta4
Fix attachment downloading

Fix issue where an attachment will only be downloaded once per
program instance not per class instance. This was caused by using
dispatch_once which should only be used for singleton set up