Bump API version of plugins that do not need extra porting

Contributes to CURA-1615

plugins/3MFReader/__init__.py

@@ -13,7 +13,7 @@ def getMetaData():
             "author": "Ultimaker",
             "version": "1.0",
             "description": catalog.i18nc("@info:whatsthis", "Provides support for reading 3MF files."),
-            "api": 2
+            "api": 3
         },
         "mesh_reader": [
             {

plugins/ChangeLogPlugin/__init__.py

@@ -13,9 +13,9 @@ def getMetaData():
             "author": "Ultimaker",
             "version": "1.0",
             "description": catalog.i18nc("@info:whatsthis", "Shows changes since latest checked version."),
-            "api": 2
+            "api": 3
         }
     }
 
 def register(app):
-    return {"extension": ChangeLog.ChangeLog()}
+    return {"extension": ChangeLog.ChangeLog()}

plugins/ImageReader/__init__.py

@@ -13,7 +13,7 @@ def getMetaData():
             "author": "Ultimaker",
             "version": "1.0",
             "description": i18n_catalog.i18nc("@info:whatsthis", "Enables ability to generate printable geometry from 2D image files."),
-            "api": 2
+            "api": 3
         },
         "mesh_reader": [
             {

plugins/RemovableDriveOutputDevice/__init__.py

@@ -13,7 +13,7 @@ def getMetaData():
             "author": "Ultimaker B.V.",
             "description": catalog.i18nc("@info:whatsthis", "Provides removable drive hotplugging and writing support."),
             "version": "1.0",
-            "api": 2
+            "api": 3
         }
     }