Remember states of groups on the "External tools" page of the "Application Settings" dialog

Scenario:

1. Open the "Application Settings" dialog.
2. Open the "External tools" page.
3. Show content of the "Custom tools" group.
4. Select another page and return to the "External tools" page.
   Current result: the content of the "Custom tools" group is hidden.
   Expected result: the content of the "Custom tools" group is shown.

States of all three groups ("Supported tools", "Custom tools", "Additional information") should be remembered. They should be kept even in case the "Application Settings" dialog is reopened or UGENE is restarted.