QImage plugins should report supported mime types

Extend JSON plugin descriptions with supported MIME types.

Task-number: QTBUG-28177

Change-Id: If8e64a4a0f052718510383a74622598d741640d3
Reviewed-by: Lars Knoll <lars.knoll@digia.com>

src/plugins/imageformats/mng/mng.json

 {
-    "Keys": [ "mng" ]
+    "Keys": [ "mng" ],
+    "MimeTypes": [ "image/x-mng" ]
 }

src/plugins/imageformats/tga/tga.json

 {
-    "Keys": [ "tga" ]
+    "Keys": [ "tga" ],
+    "MimeTypes": [ "image/x-tga" ]
 }

src/plugins/imageformats/tiff/tiff.json

 {
-    "Keys": [ "tiff", "tif" ]
+    "Keys": [ "tiff", "tif" ],
+    "MimeTypes": [ "image/tiff", "image/tiff" ]
 }

src/plugins/imageformats/wbmp/wbmp.json

 {
-    "Keys": [ "wbmp" ]
+    "Keys": [ "wbmp" ],
+    "MimeTypes": [ "image/vnd.wap.wbmp" ]
 }