crashes on Python 3.14 due to nested argument groups in argparse

Environment:

• Powerline: latest (Gentoo app-misc/powerline)
• Python: 3.14.6
• OS: Gentoo Linux

Description: powerline-daemon fails to start on Python 3.14. Python 3.14 enforces a stricter argparse contract: calling add_argument_group() on a _MutuallyExclusiveGroup now raises a ValueError instead of silently succeeding.

Traceback:

Traceback (most recent call last):
  File ".../powerline-daemon", line 495, in <module>
    main()
  File ".../powerline-daemon", line 423, in main
    parser = get_daemon_argparser()
  File ".../powerline/commands/daemon.py", line 21, in get_argparser
    replace_group = exclusive_group.add_argument_group()
  File ".../argparse.py", line 1795, in add_argument_group
    raise ValueError('argument groups cannot be nested')
ValueError: argument groups cannot be nested

Root cause: powerline/commands/daemon.py, line 21: exclusive_group.add_argument_group() — nesting an argument group inside a mutually exclusive group was never a documented argparse API and is now explicitly rejected in Python 3.14, (see cpython#127133 or similar).

Suggested fix: Add arguments directly to exclusive_group instead of creating a nested group:

# Before
replace_group = exclusive_group.add_argument_group()
replace_group.add_argument('--replace', ...)

# After
exclusive_group.add_argument('--replace', ...)

Impact: powerline-daemon is completely non-functional on Python 3.14.