Start class layouts for backups and plugins API

cura/Backups/Backup.py

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+# Copyright (c) 2018 Ultimaker B.V.
+# Cura is released under the terms of the LGPLv3 or higher.
+
+
+class Backup:
+    """
+    The backup class holds all data about a backup.
+    It is also responsible for reading and writing the zip file to the user data folder.
+    """
+
+    def __init__(self):
+        self.generated = False  # type: bool
+        self.backup_id = None  # type: str
+        self.target_cura_version = None  # type: str
+        self.zip_file = None
+        self.meta_data = None  # type: dict
+
+    def getZipFile(self):
+        pass
+
+    def getMetaData(self):
+        pass
+
+    def create(self):
+        self.generated = True
+        pass
+
+    def restore(self):
+        pass