pep8 loose compliance

[totaam]

A flake8 config was added to https://github.com/Xpra-org/xpra/blob/master/pyproject.toml in 9ab64d9.
Then lots of minor fixes in 1618eef + 8aae423 for xpra/x11, 263497a for xpra/util and 633fafa for xpra/notifications, xpra/dbus and xpra/gstreamer.

What's left as of 9fbf6db:

$ find xpra/* -maxdepth 0 -type d -exec echo -n "{}    " \; -exec bash -c "pflake8 {} | wc -l" \;
xpra/audio    0
xpra/buffers    0
xpra/client    2173
xpra/clipboard    0
xpra/codecs    737
xpra/dbus    0
xpra/gstreamer    0
xpra/gtk    795
xpra/keyboard    0
xpra/net    1237
xpra/notifications    0
xpra/platform    3200
xpra/scripts    1020
xpra/server    2594
xpra/util    0
xpra/x11    0

[totaam]

Better now:

find xpra/* -maxdepth 0 -type d -exec echo -n "{}    " \; -exec bash -c "pflake8 {} | wc -l" \; | grep -ve ' 0$'
xpra/client    2173
xpra/net    1237
xpra/platform    3200
xpra/scripts    1020
xpra/server    2594

[totaam]

Good enough for now, down to zero warnings with the config we ship, which ignores only a few modules / warnings:

xpra/pyproject.toml

Lines 29 to 53 in e10dbff

	[tool.flake8]
	max-line-length = 120
	exclude = ["xpra/gtk/examples/*.py", "xpra/platform/win32/*", "xpra/platform/darwin/*"]
	ignore = ["E203", "E231", "E225", "E226", "E252", "E221", "E741", "E262", "E265"]
	per-file-ignores = """
	xpra/audio/gstreamer_util.py:E241
	xpra/keyboard/layouts.py:E241,E501
	xpra/x11/gtk_x11/wm_check.py:E241
	xpra/x11/server/seamless.py:E241
	xpra/codecs/nvidia/util.py:E241
	xpra/codecs/loader.py:E241
	xpra/codecs/checks.py:E501
	xpra/gtk/versions.py:E241
	xpra/client/mixins/windows.py:E241
	xpra/client/gui/paint_colors.py:E241
	xpra/scripts/config.py:E241
	xpra/net/rfb/d3des.py:E241
	xpra/server/source/source_stats.py:E116,E501
	xpra/server/window/compress.py:E501
	xpra/server/mixins/fileprint.py:E241
	xpra/server/mixins/controlcommands.py:E501,E241
	xpra/platform/gui.py:E241
	xpra/platform/paths.py:E302
	xpra/platform/posix/gui.py:E241
	"""

Nothing major here:

• examples and platform modules (macos and win32)
• E203 whitespace before ':': 5504 hits
• E221 multiple spaces before operator: 351
• E231 missing whitespace after..: 2862
• E252 missing whitespace around parameter equals: 628
• E262 inline comment should start with '# ': 224
• E265 block comment should start with '# ' : 1653
• E741 ambiguous variable name..: 145