Ability to remove `ctkSettingsPanel`s from `ctkSettingsDialog`

[NogginBops]

Currently there is only an api for adding ctkSettingsPanels to ctkSettingsDialog but for reloadable plugins it would be useful to be able to remove a settings panel when the plugin is being reloaded. So I adding a ctkSettingsDialog::removePanel api would be useful.

[lassoan]

I agree, it would make sense. It would make this happen much more quickly if you could submit a pull request with the suggested change.

[NogginBops]

Done!