Prevent integer overflows for file/AIP sizes (#346)

When storing AIP and file size values, and using MySQL as the database,
file size values larger than 2GB were being stored only as 2GB. This
changes the SQLalchemy integer type, used for this data, so sizes will
be stored correctly.

AIPscan/models.py

@@ -325,7 +325,7 @@ class AIP(db.Model):
     transfer_name = db.Column(db.String(255))
     create_date = db.Column(db.DateTime(), index=True)
     mets_sha256 = db.Column(db.String(64))
-    size = db.Column(db.Integer())
+    size = db.Column(db.BigInteger())
     storage_service_id = db.Column(
         db.Integer(), db.ForeignKey("storage_service.id"), nullable=False
     )
@@ -388,7 +388,7 @@ class File(db.Model):
     filepath = db.Column(db.Text(), nullable=True)  # Accommodate long filepaths.
     uuid = db.Column(db.String(255), index=True)
     file_type = db.Column(db.Enum(FileType))
-    size = db.Column(db.Integer())
+    size = db.Column(db.BigInteger())
     # Date created maps to PREMIS dateCreatedByApplication for original
     # files, which in practice is almost always date last modified, and
     # to normalization date for preservation files.