Allow providing model_map to CDSLCorpus instance

[hrishikeshrt]

• PyCDSL version: 0.6.0
• Python version: 3.8.11
• Operating System: Ubuntu 18.04.6

Problem

• Currently, CDSLDict has a provision to specify custom models using model_map, however, the CDSLCorpus class that manages dictionaries has no provision for it.
• It makes sense to remove model_map from CDSLDict and only keep it for CDSLCorpus while keeping only lexicon_model and entry_model for CDSLDict.

Feature Description

• Add a way of specifying custom models (i.e. in CDSLCorpus) from the perspective of a programmer.
• Remove model_map from CDSLDict, add it to CDSLCorpus

Reasons

It makes sense from the end-user perspective to never really need to instantiate CDSLDict by hand, and let CDSLCorpus do it, and to that end, it makes sense that arguments required for CDSLDict are specified through the corpus class.

model_map is basically a map of lexicon and entry models per dictionary. Semantically, one dictionary does not need to be aware of the maps for other dictionaries. The map makes more sense on the corpus-management level.

[hrishikeshrt]

There is however an argument for keeping the model map in CDSLDict because it also serves the purpose of inferring models. This might be useful in future to ship custom models as part of the package.

Addition of the argument on CDSLCorpus level definitely makes sense though.