fixup! chg: generate, cleanup: Use 28 days of measurements

sbws/config.default.ini

@@ -77,7 +77,7 @@ extra_lines =
 # as defaults (currently globals.py), and just as a factor GENERATE_PERIOD.
 data_files_compress_after_days = 29
 # After this many days, delete data files.
-# 56 == 28 * 2 + 1.
+# 57 == 28 * 2 + 1.
 data_files_delete_after_days = 57
 # After this many days, compress v3bw files (1d)
 v3bw_files_compress_after_days = 1