This is a rework of the Preferences window

Glade-defined settings were replaced by list box settings.

What needs to be resolved

General notes:

• Section headers are needed to separate different settings
• Comboboxes have relief, but should be flat (white background)
• NotImplementedError when clicking on combobox rows; should open combobox?
• Mnemonics in labels to activate settings?
• 'Merge Accounts' is missing and should be added somewhere (moved from accounts window)

General page:

• PEP display settings are not implemented yet (Location, Tune, Activity, Mood; separate switch for each of these settings?)

Chat page:

• Display chatstates is not implemented yet (In Chat Tabs, In Chat Banner, and In Contact List; separate switch for each of these settings?)
• Split Chat and Group chat settings to separate pages?

Notifications page:

• Values for autopopup and notify_on_new_message are mixed in one combobox (this cannot be realized by the current setting type I think)
• auto_popup_chat_opened was not implemented (that's ok, see !433 (closed))
• autopopupaway: I would rather change that setting to 'Do Not Disturb' (and reverse the setting's value)
• notification_sign_in and notification_sign_out: I would rather have one setting about sign in/out notifications
• Sounds configuration missing (needs new setting: switch + button)
• sounddnd: I would reverse this setting to 'Do Not Disturb'; should only be enabled if play_sounds switch is active

Status page:

• To be implemented as a separate dialog? Which parts?
• Automatic status settings after timer; New setting type needed?
• restore_last_status is account-specific and should be moved to account settings
• Are both 'Ask for status message when signing in/out' needed? Is this setting actually needed at all in preferences?
• Separate dialog for preset status messages as well?

Style page:

• Manage Themes not implemented yet (css_config, New setting type needed: combobox + button)
• Dark theme setting does not get set correctly (always disabled, maybe int/str problem)
• Status icon set: custom renderer needed?

Audio/video page:

• Comboboxes are code-generated. How should we handle this?
• 'Use stun server' and server entry should be one listbox item (New setting type needed: entry + switch where entry only enabled if switch active)
• Add infobar to show dependencies if missing (or windows running)

Advanced page:

• Debug logging switch initial config value is not implemented yet
• Debugging switch should additionally have a button which opens the logs folder (switch + button)
• ACE is just one button (needs a new setting type though)