Steps to reproduce the plugin-related profile issues (running Picard from the code in the current `master` branch):

Issues #1 and #2 (Serious):

1. Start Picard.
2. Open the Options dialog and select the "Option Profiles" page. Disable any enabled profiles.
3. Create a new profile, enable the profile, and select all of the settings in the "General" section of the profile.
4. Select the "General" options page. Note that the items are highlighted (as expected).
5. Switch to the "Plugins" options page. Make a change to the plugins (enable or disable and existing plugin).
6. Swithch to the "Option Profiles" page. Note that the newly created profile (Step 3) is no longer shown. (Issue #1)
7. Switch to the "General" options page. Note that the items are still highlighted for the (Step 3) profile that is no longer available. (Issue #2)
8. Close the Options dialog using "Cancel".
9. Close Picard.

Issue #3 (Minor):

1. Start Picard.
2. Open the Options dialog and select the "Plugins" page. Disable all installed plugins.
3. Install the `dev` branch of the "Create Local Plugin" plugin. This will be used to create a local test plugin with settings that can be included in an option profile. Enable the plugin.
4. Close and restart Picard.
5. Open the Options dialog and select the "Option Profiles" page.
6. Confirm that there are no plugin settings available for inclusion in a profile. There should be no "Plugins" branch in the available settings tree for the profiles.
7. Switch to the "Plugins" > "Create Local Plugin" page, and create a local test plugin containing the "Options page and settings" template.
8. Install the test plugin (created in Step 7), and enable the plugin. Note that the options page for the plugin appears in the tree in the left pane.
9. Switch to the "Option Profiles" page.
10. Create a new profile. Note that there is now a "Plugins" branch containing your test plugin available for selection in the profile's available settings tree.
11. Enable the entire "Plugins" branch setting for the new profile. This will enable the test plugin as well as the setting that it contains.
12. Switch to the "Plugins" page, and disable the test plugin. Note that this removes the test plugin's options page from the tree in the left pane.
13. Switch to the "Options Profiles" page. Note that the new profile (created in Step 10) no longer appears (Issue #1 described above). Create a new profile, and note that there is now an empty "Plugins" branch in the available settings tree for the profile. (Issue #3)
14. Close the Options dialog using "Cancel".
15. Close and restart Picard.
16. Open the Options dialog and select the "Option Profiles" page. Note that there is no longer a "Plugins" branch in the available settings tree for the profiles.
17. Close the Options dialog using "Cancel".
18. Close Picard.