* Fix issue handling symbols with multiple inheritance.
* Remove unused code from the symbol library manager object.
* Splits out the library buffer and symbol buffer object so the can be unit
tested without having to mock the symbol library manager object.
* Add unit tests for library buffer and symbol buffer objects.
- Move PLUGIN_FILE_DESC to common.
- SCH_PLUGIN: rename Load -> LoadSchematicFile, Save -> SaveSchematicFile.
- Use PLUGIN_FILE_DESC and CanRead* in schematic plugins.
- Return none/unknown types from Find/GuessPluginType functions.
- Iterate over file types for file wildcards.
- Clean-up header checking in IO plugins.
- Use PCB plugin list in IO_MGR::GuessPluginTypeFromLibPath.
When editing or viewing library symbols, the files are watched for
underlying changes. If any occur, the user is either prompted to reload
(if reloading would overwrite their current edits) or the file is
silently updated to the current version on disk.
This also sets a custom assertion handler to avoid unneeded crashes when
recieving invalid SAMBA packets and turns off assertions entirely when
running in release (non-debug) mode