added steam icon

fixed plugin-name in CreateSteamItems.class
renamed StoreID to SteamID in SteamItem.class.php

MinecraftPayment.iml

+<?xml version="1.0" encoding="UTF-8"?>
+<module type="WEB_MODULE" version="4">
+  <component name="NewModuleRootManager" inherit-compiler-output="true">
+    <exclude-output />
+    <content url="file://$MODULE_DIR$" />
+    <orderEntry type="sourceFolder" forTests="false" />
+  </component>
+</module>