Add "overwrite endpoint" functionality

[MKaptein]

Currently, the upload() function allows for creating new endpoints but does not allow one to overwrite an existing endpoint. To make this happen we should have an update() method in the sclblpy package, and the toolchain should be updated.

See also scailable/sclbl-toolchain-server#11.

[MKaptein]

Ok, so this one is a bit more involved than I imagined initially; next to the UPDATE endpoint in the usermanager (which now exists, see scailable/sclbl-usermanager#11) we also need an UPDATE endpoint in the sclbl-toolchain-server. Furthermore, we would like:

sp.update(...., cfid, docs={}) # Update only a new version of the model
sp.update(...., cfid, docs=docs) # Update model and docs
sp.update_docs(cfid, docs) # Update only the docs

Note that for the first one we also need to check whether this (i.e., only uploading the model, not the docs, is currently an option in the usermanager).

See:

• scailable/sclbl-toolchain-server#26
• scailable/sclbl-usermanager#31

[MKaptein]

Code, tests, and docs for this to work have been added, but still needs to be tested with updated toolchain and user-manager.

[MKaptein]

Functions have now been tested together with the updates of the toolchain-server and the usermanager. All tests run (tests of the upload functionality in test_main.py).

Closing since this all seems ok!