chore(lib): re-organizing the module

This PR refactors a lot of the code in order to have a better organized codebase. If will that I needed to create a second level of submodules, to better distinguish the different parts of this project.

manim_slides/core/defaults.py

@@ -0,0 +1,8 @@
+"""Manim Slides' defaults."""
+
+from pathlib import Path
+
+FOLDER_PATH: Path = Path("./slides")
+"""Folder where slides are stored."""
+CONFIG_PATH: Path = Path(".manim-slides.toml")
+"""Path to local Manim Slides config."""