create a converter to convert the given standard from mooc [1] to lom [2]

[utnapischtim]

The MOOC platform defines a schema [1] to export the metadata. We have to create a converter to convert metadata described with this schema to LOM. This converter should be implemented with the visitor pattern like [3] and [4]. Start by implementing the [5] converter methods. Those methods should then look like "convert_image(self, value, record)". The real mapping will then be discussed

SideNote: don't use the @tc.typecheck decorator. this will be removed in the final version of this branch

[1] https://github.com/MOOChub/schema/
[2] https://en.wikipedia.org/wiki/Learning_object_metadata
[3] https://github.com/utnapischtim/invenio-rdm-pure/blob/9f46084341b86f1cd8a99064963cd215bbc98fc7/invenio_rdm_pure/converter.py#L16
[4] https://github.com/utnapischtim/invenio-rdm-pure/blob/9f46084341b86f1cd8a99064963cd215bbc98fc7/invenio_rdm_pure/converter.py#L44
[5] https://github.com/utnapischtim/invenio-rdm-pure/blob/9f46084341b86f1cd8a99064963cd215bbc98fc7/invenio_rdm_pure/converter.py#L48

[utnapischtim]

mapping MOOC -> LOM

name -> general.title
courseCode
courseMode
abstract -> general.description[]
description -> general.description[]
languages -> general.language[]
startDate
availableUntil
endDate
image -> custom.thumbnail
video ->
instructors -> metametadata.contribute
learningobjectives -> educational.description
duration -> technical.duration
partnerInstitute -> metametadata.contribute
moocProvider
url -> technical.location
workload
courseLicenses -> rights.copyrightandotherrestrictions
access