timetag/ETA: ETA 0.9.0

1. backend: introducing the new Task API
2. backend: Allow opening the file using memory mapping (mmap), by default off.
3. toolkit: Fixes Simulate growth
4. toolkit: Enable clipping of file in the initial evaluation in the toolkit.
5. toolkit: Fixes an error in the live option to plot using bokeh.
6. testing: add Python 3.9 support
7. gui: added animated eta logo
8. gui: Reload the cached GUI everytime, to avoid being stuck on older GUI versions in electron

This release coincides with the publication of our paper Z. Lin et al (2021 JINST 16 T08016) describing the ideas behind ETA.