Some localization cleanup and doc to aid in customization:

* added locale/en/LC_MESSAGES/statusnet.po to make it easier to start customizing English texts
* added notes to locale/README about customizing and how to disable languages you haven't customized
* renamed PO templates from *.po to *.pot to match general conventions and reduce confusion for people trying to find which file they're supposed to edit

scripts/update_po_templates.php

@@ -34,7 +34,7 @@ function update_core($dir, $domain)
 xgettext \
     --from-code=UTF-8 \
     --default-domain=$domain \
-    --output=locale/$domain.po \
+    --output=locale/$domain.pot \
     --language=PHP \
     --add-comments=TRANS \
     --keyword="_m:1,1t" \
@@ -64,7 +64,7 @@ function do_update_plugin($dir, $domain)
 xgettext \
     --from-code=UTF-8 \
     --default-domain=$domain \
-    --output=locale/$domain.po \
+    --output=locale/$domain.pot \
     --language=PHP \
     --add-comments=TRANS \
     --keyword='' \