Removing plugin causes error if custom keymap was based on plugin keymap

[amibiz]

After removing the plugin, if a custom keymap was created based on the plugin keymaps, an error notification is shown

Because the cloned keymap uses the ErgoKeys (QWERTY) keymap as parent, after uninstalling the plugin, IntelliJ can not find the parent keymap and shows the error notification.

Steps to reproduce:

1. Install the plugin
2. Create custom keymap based on ErgoKeys (QWERTY) by duplicating it
3. Uninstall the plugin

Workaround: delete any custom keymap based on the plugin before/after removing the plugin

Related to #30