Add alibi-detect version to metadata

[arnaudvl]

No description provided.

[jklaise]

Check alibi for an example of setting it, the module also has code for validating and raising a warning if mismatched upon loading: https://github.com/SeldonIO/alibi/blob/90ff57ed7d81bbfcbc8c544fda1472418356f293/alibi/saving.py#L93

[jklaise]

To do this properly we would also have to do #216. To clarify, if we fetch the __version__ string from alibi.version at the time of saving the detector (the object doesn't have an associated version attribute), what can happen is the following:

• Detector gets saved and obtains a _version: 0.7.2 entry in the meta attribute
• Detector gets loaded in a new version of the library, we check and raise a warning
• Detector gets saved again and because of fetching the runtime __version__ it's version entry is updated _version: 0.7.3
  This is misleading and can lead to broken artefacts because we've overwritten the version with the new (wrong) runtime value.

The better way to do is is an in alibi (see above), where each detector gets a _version class attribute upon declaration of the class. Then this is fetched upon saving and added to metadata. When a detector is reloaded in a different version a warning is issued and when it is re-saved, the correct (old) _version is fetched from the detector class attribute (the whole class is serialized by dill so this is not over-written by the new runtime class definition) and saved, so we avoid overwriting the version in the detector metadata with the incorrect (runtime) version.

[jklaise]

Tinkering with alibi I noticed that this doesn't actually work as intended and a previously-saved explainer loaded into a new alibi version is assigned the new (incorrect) version attribute.

One easy way to fix this is instead of raising a warning just raise an exception and completely disallow trying to use an artefact with a different version of the library.