Update code for compatibility with MONAI 0.2.0

[martaranzini]

Current version of the code works with MONAI version: 0.1.0+84.ga683c4e.dirty.
Need to update it to work with the (stable) release 0.2.0.
The following tasks should be addressed:

• Verify the current code can still work with MONAI 0.2.0

• Modify the code to include newer features from MONAI (e.g. Inferers)

• Develop unit-tests towards CI

[martaranzini]

Merge #7 addressed the first point of this issue and some aspects of the second bullet point.
Further work is needed to incorporate other new features and to develop proper unit-testing.

[tvercaut]

Note that this should now target MONAI 0.3