Release icewm-2.8.0

Improve the explanation on how to spy on client messages with icesh.
When rearranging windows with tile placement or cascade placement, correct for
the top side vertical offset, in those themes which have a masked top border.
Improve the explanation for some of the preferences.
Update the winoptions example on DockApps.
Guard against a color name being set to the empty string (bbidulock/icewm#614).
Improve the performance and scalability of the window list menu.
In the window list window group similar application windows together.
Add +group and +Class select options to icesh.
Improve the filtering on the WM_CLASS property in icesh.
Fix the OSS/ALSA defaults in icesound help message (bbidulock/icewm#609).
Fix the OSS/ALSA defaults in icesound man page (bbidulock/icewm#608)
Only support SVG for icons, not for icewmbg backgrounds.
Let icewmbg pixmaps free its associated Image to reduce memory usage.
Prevent a potential trailing -I flag in CMake for issue #57.
Fix the description for sizeby in the icesh manpage.
Fix overflows in battery calculations for issue bbidulock/icewm#607.
Update the translations, most notably Brazilian Portuguese.

shasum icewm-2.8.0.tar.lz a08e55e9213997aa657540113623b6afabf71ac7