refactor code
- move handlebars to kult2e.js
- remove override of _render()
- drastically shorten _toggleEditMode()
- remove _toggleEditModeWrapper()
- move edit mode boolean marker to actor.data.data
- replace all (viewmode|editmode) classes in .hbs with if-handlebars
- remove .window-app and .window-content selectors from charsheets for compatibility with gm-screen module (https://github.com/ElfFriend-DnD/foundryvtt-gmScreen/issues/66) ToDo: remove the (viewmode|editmode) classes altogether and wrap the individual blocks/elements directly