Also fixes a bug where an empty window would get left when loading
a file from the KiCad manager window errored out.
Also fixes a bug where we were getting the wrong exception because
we were rethrowing the type-casted one (rather than just calling
throw).
Fixes https://gitlab.com/kicad/code/kicad/issues/8604
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