Move -app-name variable to brand.ftl

So a custom build doesn't have to modify each .ftl file

`app-name` is redundant with the Firefox strings, but it's what we used
previously and is easier to remember.

app/assets/branding/locale/brand.ftl

@@ -3,4 +3,5 @@
 -brand-full-name = Zotero
 -brand-product-name = Zotero
 -vendor-short-name = Zotero
-trademarkInfo = Zotero is a trademark of the Corporation for Digital Scholarship.
+-app-name = Zotero
+trademarkInfo = Zotero is a trademark of the Corporation for Digital Scholarship.

chrome/content/zotero/elements/base.js

@@ -42,6 +42,7 @@ class XULElementBase extends XULElement {
 			this.append(content);
 		}
 
+		MozXULElement.insertFTLIfNeeded("branding/brand.ftl");
 		MozXULElement.insertFTLIfNeeded("zotero.ftl");
 		if (document.l10n && this.shadowRoot) {
 			document.l10n.connectRoot(this.shadowRoot);

chrome/content/zotero/import/importWizard.xhtml

@@ -10,6 +10,7 @@
 		onload="Zotero_Import_Wizard.init()"
 >
 	<linkset>
+		<html:link rel="localization" href="branding/brand.ftl" />
 		<html:link rel="localization" href="zotero.ftl" />
 	</linkset>
 

chrome/content/zotero/publicationsDialog.xhtml

@@ -33,6 +33,7 @@
 		onload="Zotero_Publications_Dialog.init()"
 >
 	<linkset>
+		<html:link rel="localization" href="branding/brand.ftl" />
 		<html:link rel="localization" href="zotero.ftl" />
 	</linkset>
 	

chrome/content/zotero/rtfScan.xhtml

@@ -10,6 +10,7 @@
 		onload="Zotero_RTFScan.init()"
 >
 	<linkset>
+		<html:link rel="localization" href="branding/brand.ftl" />
 		<html:link rel="localization" href="zotero.ftl" />
 	</linkset>
 	

chrome/locale/en-US/zotero/zotero.ftl

@@ -1,5 +1,3 @@
--app-name = Zotero 
-
 import-wizard =
     .title = "Import"