Make appdata file translatable. Bug 713937.

* desktop/CMakeLists.txt: Translate the appdata file rather than just
  installing it directly.

* desktop/geary.appdata.xml.in: Rename from 'geary.appdata.xml', make
  name, summary and description translatable.

* cmake/FindIntltool.cmake: Add a CMake command for the appdata file.

* po/POTFILES.in: Include geary.appdata.xml.in.

desktop/CMakeLists.txt

@@ -2,14 +2,13 @@
 # Build and install geary.desktop
 #
 
-install(FILES geary.appdata.xml DESTINATION share/appdata)
-
 include (FindIntltool)
 include (FindDesktopFileValidate)
 if (INTLTOOL_MERGE_FOUND)
+    INTLTOOL_MERGE_APPDATA (geary.appdata.xml po)
     INTLTOOL_MERGE_DESKTOP (geary.desktop po)
     INTLTOOL_MERGE_AUTOSTART_DESKTOP (geary-autostart.desktop po)
-    
+
     if (DESKTOP_VALIDATE)
         if (DESKTOP_FILE_VALIDATE_FOUND)
             VALIDATE_DESKTOP_FILE (geary.desktop)

desktop/geary.appdata.xml.in

@@ -5,26 +5,26 @@
   <id>geary.desktop</id>
   <metadata_license>CC0-1.0</metadata_license>
   <project_license>LGPL-2.1+</project_license>
-  <name>Geary</name>
-  <summary>Send and receive email</summary>
+  <_name>Geary</_name>
+  <_summary>Send and receive email</_summary>
   <description>
-    <p>
+    <_p>
       Geary is an email application built around conversations, for
       the GNOME 3 desktop. It allows you to read, find and send email
       with a straightforward, modern interface.
-    </p>
-    <p>
+    </_p>
+    <_p>
       Conversations allow you to read a complete discussion without
       having to find and click from message to message.
-    </p>
-    <p>Geary's features include:</p>
+    </_p>
+    <_p>Geary's features include:</_p>
     <ul>
-      <li>Quick email account setup</li>
-      <li>Shows related messages together in conversations</li>
-      <li>Fast, full text and keyword search</li>
-      <li>Full-featured HTML and plain text message composer</li>
-      <li>Desktop notification of new mail</li>
-      <li>Compatible with GMail, Yahoo! Mail, Outlook.com and other IMAP servers</li>
+      <_li>Quick email account setup</_li>
+      <_li>Shows related messages together in conversations</_li>
+      <_li>Fast, full text and keyword search</_li>
+      <_li>Full-featured HTML and plain text message composer</_li>
+      <_li>Desktop notification of new mail</_li>
+      <_li>Compatible with GMail, Yahoo! Mail, Outlook.com and other IMAP servers</_li>
     </ul>
   </description>
   <url type="homepage">https://wiki.gnome.org/Apps/Geary</url>