REL: v3.5.1

This is the first bugfix release of the 3.5.x series.

This release contains several critical bug-fixes:

* fix installation issues when setting a default backend
* fix `add_lines` on horizontal colorbars
* fix `streamplot` with start points on right or top edge
* fix colorbars with boundaries or NoNorm
* fix colorbars with negative contours
* fix colorbars with tight layout
* fix setting Axis label alignment to center
* fix subfigure tight bounding box
* fix subplot parameter window on macosx backend
* fix unit handling in `Collections.set_offsets`
* fix unyt integration in `errorbar`
* re-display date offset in `ConciseDataFormatter` after zoom
* reduce `do_3d_projection` deprecation warnings in external artists