Closes #297, Toolbar button 'S' needs to be replaced with 'Z'

Icons from Ken

Of course, I realized just now that this is really quite similar to the stop sign, and anyone who puts this to the left of their URL bar and doesn't have a Home icon in their toolbar will get the two next to each other... Looks good otherwise, though.

chrome/chromeFiles/content/scholar/overlay.xul

@@ -23,7 +23,7 @@
 		<command id="cmd_scholar_search" oncommand="ScholarPane.search();"/>
 	</commandset>
 	<toolbarpalette id="BrowserToolbarPalette">
-		<toolbarbutton id="scholar-toolbar-button" class="toolbarbutton-1"
+		<toolbarbutton id="zotero-toolbar-button" class="toolbarbutton-1"
 						label="&scholar.name;"
 						oncommand="ScholarPane.toggleDisplay();"/>
 	</toolbarpalette>

chrome/chromeFiles/skin/default/scholar/scholar.css

@@ -1,41 +1,31 @@
-#scholar-toolbar-button
+#zotero-toolbar-button
 {
-	list-style-image: url('chrome://scholar/skin/toolbar-large.png');
+	list-style-image: url('chrome://scholar/skin/zotero-z-24px.png');
 }
 
-#scholar-toolbar-button:active
+#zotero-toolbar-button:hover
 {
-	list-style-image: url('chrome://scholar/skin/toolbar-large-active.png');
+	list-style-image: url('chrome://scholar/skin/zotero-z-24px-hover.png');
 }
 
-#scholar-toolbar-button[disabled="true"]
+#zotero-toolbar-button:active
 {
-	list-style-image: url('chrome://scholar/skin/toolbar-large-disabled.png');
+	list-style-image: url('chrome://scholar/skin/zotero-z-24px-active.png');
 }
 
-toolbar[iconsize="small"] #scholar-toolbar-button
+toolbar[iconsize="small"] #zotero-toolbar-button
 {
-	list-style-image: url('chrome://scholar/skin/toolbar-small.png');
+	list-style-image: url('chrome://scholar/skin/zotero-z-16px.png');
 }
 
-toolbar[iconsize="small"] #scholar-toolbar-button:active
+toolbar[iconsize="small"] #zotero-toolbar-button:hover
 {
-	list-style-image: url('chrome://scholar/skin/toolbar-small-active.png');
+	list-style-image: url('chrome://scholar/skin/zotero-z-16px-hover.png');
 }
 
-toolbar[iconsize="small"] #scholar-toolbar-button[disabled="true"]
+toolbar[iconsize="small"] #zotero-toolbar-button:active
 {
-	list-style-image: url('chrome://scholar/skin/toolbar-small-disabled.png');
-}
-
-#scholar-toolbar-button
-{
-	list-style-image: url('chrome://scholar/skin/toolbar-large.png');
-}
-
-toolbar[iconsize="small"] #scholar-toolbar-button
-{
-	list-style-image: url('chrome://scholar/skin/toolbar-small.png');
+	list-style-image: url('chrome://scholar/skin/zotero-z-16px-active.png');
 }
 
 textbox[multiline="true"][type="timed"]