Visual timeline loading speedups

[Jowan-Spooner]

PR, that tries to speedup the loading of visual timelines.

While still far from optimal, this PR makes it so the body of events that have their body hidden by default is only build, once that body is opened.

Other changes:

• removed left and right labels from event fields and add labels only when needed (to remove unnecessary nodes)
• removed some not needed nodes from EventBlock scene
• removed Popup window node from event block scene
• played around with visual timeline style (sorry, couldn't help it)
• added a lot of static typing hints
• changed it so get_property_list is no longer used (new method name is get_event_editor_info) for storing the event editor fields, hopefully reducing the calls this method gets

ToDo:

• reimplement popup window (this time only one node for all events)

Because the adding of nodes to the scene tree is the most intensive action during the loading this already speeds it up, especially for events with many body settings (like character, position and choice). More could possibly be removed by using draw commands (e.g. for icons) instead of nodes, especially on the Complex Picker (which is used in the condition picker for example).

[Jowan-Spooner]

Would appreciate if someone with a "real" project could test this and let me know if the experience has improved for them, when opening long timelines.