Bw-timex

* Handled emissions occuring outside of fixed time horizon in dynamic characterization [46](https://github.com/brightway-lca/bw_timex/issues/46)
* Fix substitution exchanges [53](https://github.com/brightway-lca/bw_timex/issues/53)
* Fix non-unitary production exchanges [55](https://github.com/brightway-lca/bw_timex/issues/55)

* Renamed repo and package to bw_timex
* Fixed error in dynamic characterization if IDs were stored as flow identifiers in methods

* Update to match Bugfix in [bw_temporalis v1.1](https://github.com/brightway-lca/bw_temporalis/commit/5ec8c850f325f6b5aa88cd2357bb56401304ddda): static_activity_indices are database IDs instead of matrix IDs

* Improved user-friendliness for SETAC

* Inital version with core functionalities