fix item prop dlg loses name icon
custom Application chooser mime context
session dont save default menu labels and icons

This will make session files smaller and will allow updated translations of
menu item names to be seen so long as the user did not change the name.

NOTE:  As a result of this change, when downgrading to older spacefm versions,
customized menu item names and icons of built-in items will be lost (custom
menu items will not be affected).
item prop App add Choose/Browse #306
design menu add New|Import
item prop dlg for toolbar items
fix command line with tabs