1) don't ASSERT; use exceptions (which can be caught) instead.
2) clean up LIB_LOGGER so it's only used during sync
3) fix typos in wxLogMessage() calls so they produce output.
4) throw on unrecognized token in loadContent().
5) if clipboard can't be pasted as content then paste as text.
Fixes: lp:1840172
* https://bugs.launchpad.net/kicad/+bug/1840172
wxLog::SetActiveTarget() was initialised to libedit frame,
but the active target was not released after closing and deleting libedit, thus creating a crash on Kicad exit.
A bug in LIB_MANAGER::LibraryExists() prevented a library removed from
the symbol library table from being removed from the tree view. Add the
proper check to SYMBOL_TREE_SYNCHRONIZING_ADAPTER::Sync().
This exposed another issue with synchronization between the library
table editor and the tree view which could lead to orphaned library
modifications and/or a segfault when the currently selected library was
removed from the symbol library table. Give the user a chance to save
or revert any changes before allowing changes to the symbol library
table.
Fixes lp:1821691
https://bugs.launchpad.net/kicad/+bug/1821691
Jeff Young
jean-pierre charras
Wayne Stambaugh
Tomasz Wlostowski