Issue #1479652 by Psikik, jhedstrom: Convert image style config filenames/keys...

Issue #1479652 by Psikik, jhedstrom: Convert image style config filenames/keys from plural to singular.

core/modules/image/config/image.style.large.xml

+<?xml version="1.0"?>
+<config>
+  <name>large</name>
+  <effects>
+    <image_scale_480_480_1>
+      <name>image_scale</name>
+      <ieid>image_scale_480_480_1</ieid>
+      <data>
+        <width>480</width>
+        <height>480</height>
+        <upscale>1</upscale>
+      </data>
+      <weight>0</weight>
+    </image_scale_480_480_1>
+  </effects>
+</config>

core/modules/image/config/image.style.medium.xml

+<?xml version="1.0"?>
+<config>
+  <name>medium</name>
+  <effects>
+    <image_scale_220_220_1>
+      <name>image_scale</name>
+      <ieid>image_scale_220_220_1</ieid>
+      <data>
+        <width>220</width>
+        <height>220</height>
+        <upscale>1</upscale>
+      </data>
+      <weight>0</weight>
+    </image_scale_220_220_1>
+  </effects>
+</config>

core/modules/image/config/image.style.thumbnail.xml

+<?xml version="1.0"?>
+<config>
+  <name>thumbnail</name>
+  <effects>
+    <image_scale_100_100_1>
+      <name>image_scale</name>
+      <ieid>image_scale_100_100_1</ieid>
+      <data>
+        <width>100</width>
+        <height>100</height>
+        <upscale>1</upscale>
+      </data>
+      <weight>0</weight>
+    </image_scale_100_100_1>
+  </effects>
+</config>