UI: support light/dark mode

src/AccRingGeneralVC.mm

src/AccountSettingsVC.mm

src/ChatVC.mm

src/ConversationVC.mm

src/PreferencesWC.mm

src/RingWindowController.mm

src/RingWizardWC.mm

src/SmartViewVC.mm

src/views/AccountMenuItemView.mm

src/views/HoverTableRowView.h

src/views/HoverTableRowView.mm

src/views/IMTableCellView.mm

src/views/IconButton.mm

src/views/MessageBubbleView.mm

src/views/RoundedTextField.mm

ui/Base.lproj/AccAdvancedRing.xib

ui/Base.lproj/AccAdvancedSip.xib

ui/Base.lproj/AccRingGeneral.xib

ui/Base.lproj/AccSipGeneral.xib

ui/Base.lproj/AccountSettings.xib