misc: add parametrizable colors for theme support

src/mainview/components/ContactPicker.qml

src/mainview/components/ContactPickerItemDelegate.qml

src/mainview/components/ContactSearchBar.qml

...view/components/ConversationSmartListViewItemDelegate.qml

src/mainview/components/MediaHandlerItemDelegate.qml

src/mainview/components/MediaHandlerPicker.qml

src/mainview/components/MessageWebView.qml

src/mainview/components/MessageWebViewHeader.qml

src/mainview/components/RecordBox.qml

src/mainview/components/SidePanel.qml

src/mainview/components/UserProfile.qml

src/mainview/components/WelcomePage.qml

src/settingsview/SettingsView.qml

src/settingsview/components/AccountProfile.qml

src/settingsview/components/AdvancedMediaSettings.qml

src/settingsview/components/AdvancedNameServerSettings.qml

src/settingsview/components/AdvancedOpenDHTSettings.qml

...settingsview/components/AdvancedPublicAddressSettings.qml

src/settingsview/components/AdvancedSettings.qml

src/settingsview/components/AvSettingPage.qml