Fixed coupled of issues

[MFSY]

• forge.prefixes() was raising pandas.Dataframe error "if using all scalar values, you must pass an index"
• fixed forge.types() to properly collect types from rdfsercice.class_to_shape
• fixed forge.template() when using an rdf model based on a store service: Unable to generate template:'tuple' object has no attribute 'traverse'

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 73.33333% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 75.57%. Comparing base (e31eb27) to head (5efef34).

Files	Patch %	Lines
kgforge/core/archetypes/model.py	55.55%	4 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #394 +/- ## ========================================== + Coverage 75.52% 75.57% +0.04% ========================================== Files 103 103 Lines 6643 6644 +1 ========================================== + Hits 5017 5021 +4 + Misses 1626 1623 -3 ``` | [Flag](https://app.codecov.io/gh/BlueBrain/nexus-forge/pull/394/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BlueBrain) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/BlueBrain/nexus-forge/pull/394/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BlueBrain) | `75.57% <73.33%> (+0.04%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BlueBrain#carryforward-flags-in-the-pull-request-comment) to find out more.

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