When no default library tables are found, set the default wxFilePickerCtrl
to the users configuration path instead of the current project path to
prevent any project library tables from being used as the default.
Fixes lp:1809769
https://bugs.launchpad.net/kicad/+bug/1809769
Factor out common dialog code from global symbol library table dialog for
loading initial library table.
Update global symbol library table code to user factored out common dialog
code.