Exmol

- Added synspace method to generate synthetically feasible space
- Added drug-like filter by default for counterfactuals

* Fixed bug in sorting for text explanations
* Fixed empty plot names saying None
* Added priority for naming and removed invalid names
* Added more names (metyhl, ethyl, butyl, etc)
* Fixed sample_space to accept partials or objects
* Added openai prompting
* Added name_morgan_bit as external facing

* Added natural language explanation method
* Added names to ECFP plots and naming of ECFP fragments

* Fixed bug in `plot_descriptors`

* `plot_descriptors` will no longer save to file without filename

Made default run_stoned argument use basic instead of semantically robust alphabet, as claimed in documentation