Fix attachments download by using EmailStore.get
Fix attachments download by using EmailStore.get

Flask uses client-side sessions which are limited to 4kb in size. This
means that the previous attachments retrieval approach (based on storing
the attachments in the session) doesn't work for large attachments.

ascoderu/opwen-webapp,OPWEN/opwen-webapp,ascoderu/opwen-webapp,OPWEN/opwen-webapp,ascoderu/opwen-cloudserver,ascoderu/opwen-cloudserver,OPWEN/opwen-webapp,ascoderu/opwen-webapp