Add settings page for Panels

This adds a settings page for the dolphin panels in the settings as discussed in !719 (closed)

For now this just includes the settings for the information panel and keeps the context menu for it.

I also moved the information panel settings from "dolphin_informationpanelsettings" to "dolphin_generalsettings" because most other settings from the dolphin settings are stored there. If this is unwanted or not how this is normally done, I can revert it.

Before	After
(The theme looks different in my installed and self-compiled version)

The settings page is missing the "configure" button for the entries in the information panel, which can only be found in the context menu. This is because I thought it would be weird to move it to the settings page. (The "configure" button is used to select the entries for the information panel)