Extract _write_bundle to omf.persist

- Add support for persisting theme information.
- Use documented private function naming scheme.

pkg/omf/cli/omf.install.fish

 function omf.install -a type_flag name_or_url
-  function _write_bundle
-    set bundle $OMF_CONFIG/bundle
-    set record $argv
-
-    if test -f $bundle
-      if not grep $record $bundle > /dev/null 2>&1
-        echo $record >> $bundle
-      end
-    else
-      echo $record > $bundle
-    end
-  end
-
   function _display_success
     echo (omf::em)"✔ $argv successfully installed."(omf::off)
   end
@@ -42,7 +29,7 @@ function omf.install -a type_flag name_or_url
     else
       echo (omf::dim)"Trying to clone from URL..."(omf::off)
       if git clone -q $name_or_url $OMF_PATH/$parent_path/$local_name
-        _write_bundle "$install_type $name_or_url"
+        omf.persist $install_type $name_or_url
         _display_success "$install_type $name_or_url"
       else
         _display_error "$install_type $name_or_url"
@@ -60,7 +47,7 @@ function omf.install -a type_flag name_or_url
   else
     echo (omf::dim)"Installing $name_or_url $install_type..."(omf::off)
     if git clone (cat $OMF_PATH/db/$target) $OMF_PATH/$target >/dev/null ^&1
-      _write_bundle "$install_type $name_or_url"
+      omf.persist $install_type $name_or_url
       _display_success "$install_type $name_or_url"
     else
       _display_error "$install_type $name_or_url"

pkg/omf/cli/omf.persist.fish

+function omf.persist -a type name_or_url
+  function __omf.write_bundle
+    set -l bundle $OMF_CONFIG/bundle
+    set -l record $argv
+
+    if test -f $bundle
+      if not grep $record $bundle > /dev/null 2>&1
+        echo $record >> $bundle
+      end
+    else
+      echo $record > $bundle
+    end
+  end
+
+  function __omf.write_theme
+    echo $argv > $OMF_CONFIG/theme
+  end
+
+  __omf.write_bundle "$type" "$name_or_url"
+  if test "$type" = theme
+    __omf.write_theme "$name_or_url"
+  end
+end