Release icewm-3.1.0

Add a winoption "frame" to automatically group application windows
with the same "frame" value as tabs in a single frame.
Show indicators for the presence of tabs on the title bar.
Click on the title bar tab indicators to change tabs.
Give each tab its own set of winoptions.
Fix for merging a transient window as a tab to its owner window.
Preserve tray hints across restarts.
Preserve tabs across restarts.
Improve the Alt+Tab for tabbed frames for issue bbidulock/icewm#673.
When switching tabs, ensure that focus is preserved.
Add a MouseWinTabbing preference to merge tabs for #95.
Let the window list support tabs.
Various improvements to the CMake build.
Updated translations: French, Portuguese (Brazil).

shasum icewm-3.1.0.tar.lz 37ef489238fdd29de64128b89c52056e05904f33