Filter splicing on expression

- Add `Study.tidy_splicing_with_expression` `@cached_property()` of a tidy dataframe of splicing events, that have known gene annotations
- Add `Study.filter_splicing_on_expression` method
- Add option to give `expression_thresh` for `Study.modalities` and `Study.modalities_counts` and `Study.plot_lavalamp_pooled_inconsistent`, then `Study` will do the filtering for you

Todo:

- [ ] Add release notes
- [ ] Add gallery?