Pytransform3d

Fixes broken installation of subpackages in version 1.9.

**Warning**

This release is broken. Subpackages will not be installed. Use 1.9.1.

**Refactoring**

* Large modules are split into multiple files (non-breaking change)
* Refactoring of URDF parser
* Matplotlib is not strictly necessary anymore to use the core code of pytransform3d without its plotting features

**Features**

* Adds type hints for static type checking in additional type stubs (files with ending .pyi)
* Adds `trajectories.invert_transforms` to invert multiple transformation matrices at once
* Adds function to parse inertial tag in URDF
* Makes some validations before conversions optional
* Adds option to visualize ellipsoid
* Adds rotors as a new concept to represent rotations

**Bugfixes**

* Fixes numerical issue in conversion from matrix to axis-angle representation

* Adds unit dual quaternions as a new representation of transformations.
* Adds batch operations on unit dual quaternions.
* Adds screw linear interpolation (ScLERP) for dual quaternions.
* Adds functions to visualize and plot a camera configuration in 3D.
* Adds function to remove an artist from the Open3D visualizer.
* Fixes deprecation warnings of numpy and matplotlib.

* Clean up 3D plots in matplotlib (no gray background, less ticks)
* Documentation target latexpdf works now as SVG images were replaced by PNGs. This also fixes missing font issues in the HTML documentation.

* Adds batch conversions of orientation and pose representations and similar operations
* Adds function `norm_exponential_coordinates`
* Adds tables of content for longer documentation pages
* Prints more useful warning for missing mesh filename in `pytransform3d.plot_utils.plot_mesh`
* Makes frames of collision objects and visuals unique in UrdfTransformManager

* Adds all 24 Euler angle conventions (conversion to rotation matrix and from rotation matrix)
* Adds option to convert 'package://' in URDF files to a specified directory
* Adds options to control appearance of collision objects and visuals in plots: wireframe, convex hull, alpha value
* Compute vertex normals of meshes before rendering
* Fixes visualization of TransformManager