Reduce action bar icons size from 48dp to 24dp

From the Material Design spec:

> DP unit grid

> System icons are displayed at 24dp.

See http://www.google.com/design/spec/style/icons.html#icons-system-icons

Script used to update the icons:

    function download {
        F-Droid/tools/download-material-icon.sh F-Droid/res $1 $2
    }

    download content add
    download device bluetooth
    download action delete
    download notification do_not_disturb
    download image edit
    download action help
    download device nfc
    download av play_arrow
    download navigation refresh
    download action search
    download action settings
    download social share
    download action view_headline

F-Droid/tools/download-material-icon.sh

@@ -17,7 +17,7 @@ function usage {
 function download {
 	REMOTE_DRAWABLE_DIR=$1
 	LOCAL_DRAWABLE_DIR=$2
-	FILE="ic_${ICON}_48dp.png"
+	FILE="ic_${ICON}_24dp.png"
 	URL="$BASE_URL/$CATEGORY/$REMOTE_DRAWABLE_DIR/$FILE"
 	DIR="$RES_DIR/$LOCAL_DRAWABLE_DIR"