Changes:
- BREAKING: dropped support for Python 3.7
- new function: [navis.pop3d()](https://navis.readthedocs.io/en/latest/source/generated/navis.pop3d.html#navis.pop3d) removes the most recently added object from the vispy 3d viewer
- new experimental functions for (pairwise) alignment of neurons using the pycpd package: [navis.nblast_align()](https://navis.readthedocs.io/en/latest/source/generated/navis.nblast_align.html#navis.nblast_align), `navis.align.align_deform()`, `navis.align.align_rigid()`, `navis.align.align_pca()`, `navis.align.align_pairwise()`
- [navis.xform_brain()](https://navis.readthedocs.io/en/latest/source/generated/navis.xform_brain.html#navis.xform_brain) now recognizes the target template’s units if available
- new NeuronList method: `navis.NeuronList.set_neuron_attributes()`
- new utility functions: [navis.nbl.compress_scores()](https://navis.readthedocs.io/en/latest/source/generated/navis.nbl.compress_scores.html#navis.nbl.compress_scores), `navis.nbl.nblast_prime()`
- improved persistence functions: [navis.persistence_distances()](https://navis.readthedocs.io/en/latest/source/generated/navis.persistence_distances.html#navis.persistence_distances), `navis.persistence_vector()`, `navis.persistence_diagram()`
- [navis.longest_neurite()](https://navis.readthedocs.io/en/latest/source/generated/navis.longest_neurite.html#navis.longest_neurite) and [navis.cell_body_fiber()](https://navis.readthedocs.io/en/latest/source/generated/navis.cell_body_fiber.html#navis.cell_body_fiber) now also allow removing the longest neurite and CBF, respectively
- [navis.heal_skeleton()](https://navis.readthedocs.io/en/latest/source/generated/navis.heal_skeleton.html#navis.heal_skeleton) now accepts a mask parameter that allows restricting where fragments are stitched
- various other bugfixes