Imgui-bundle

Please use v0.8.7 instead

Hello ImGui and ImmApp usability improvements:
* customize menu App
* Docking Layout: keep user preferences
* improve windows initial layout

Added python bindings for implot_internal

Minor improvements:
- Improve font rendering
- Improve emscripten idling mode
- Review main theme (DarculaDarker) to make it easier on the eyes

* Autoresize window post startup
* Corrected notebook rendering

* correct launch demo_node_editor_basic

* markdown: render code blocks with text editor, and make them easily copyable
* add lots of demos
* add doc / ascii_doc
* add emscripten interactive manual
* add immapp::snippets
* add portable_file_dialogs