Brainweb

- fix `get_mmr_fromfile` arguments being ignored (5 <- 3)
- fix `toPetMmr` ignoring `modes` (7)
- cache & make configurable: resolution & PET activity class (8, 6 <- 4)
- add `get_label_probabilities() (8 <- 2)
- add `Act.all_labels`
- expose `Act`
- add `trim_zeros_ROI()`
- make `toPetMmr()` return `ndarray`
- update example images
- update dependencies

- suppress `volshow` tight layout warning
- misc minor framework updates

- fix PET/mu map intensities
- update documentation
- add `pip install brainweb[register]` convenience

- add `register`
- fix python3
- update documentation

- auto-clear unused axes
- add `Amyloid`
- expose `PetClass` and other intensities
- minor documentation update

- `volshow` updates
+ allow repeat `tight_layout`
+ `fontproperties`
+ `frameon=False` (fully borderless)
- executable `setup.py`