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.styles.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.styles.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.styles.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>