Fix alibi-explain-server to use alibi load_explainer helper function

[seldondev]

Currently alibiexplainer v1 server isloadingexplainer artefacts using dill.load

Given that alibi is now using load_explainer and save_explainer we have to use these methods instead.Otherwise things are likely to break. For example AnchorImage is expected to be broken currently given that save_explainer will persist a separate dill for the segmentation_fn

If we use load_explainer, internally there is a call to reset_predictor, so we also need to remove that fromalibi-explain-server

Also we need to update / fix tests: e.g.test_anchor_images.py

• docs to reflect any instructions that we exposed to users.