Add CLI argument for selecting banks

When debugging a failure for one bank's website, I often want to run
the fetch for just that bank.  To date, I've been commenting out the
other bank, but that is silly.  Now, `xactfetch` can target a subset
of banks by specifying their name slug(s) as CLI arguments.

xactfetch.py

@@ -6,6 +6,7 @@ import json
 import logging
 import os
 import random
+import sys
 import subprocess
 import urllib.parse
 from pathlib import Path
@@ -690,8 +691,11 @@ def main() -> None:
         browser = pw.firefox.launch(headless=headless)
         page = browser.new_page()
         failed = False
+        banks = sys.argv[1:] or list(ACCOUNTS.keys())
+        if 'commerce' in banks:
             if not download_commerce(page, end_date, token, importer):
                 failed = True
+        if 'chase' in banks:
             if not download_chase(page, end_date, token, importer):
                 failed = True
     raise SystemExit(1 if failed else 0)