[Enhancement] Check data types in load_model method

[raoulcollenteur]

trafficstars

Describe the bug The data types are not well checked when reading a pastas model from a .pas file. See for example this issue in the Pastastore:

https://github.com/pastas/pastastore/issues/39

A name is a string, but load_model with return an integer of only numbers are provided.

Expected behavior Data types should be the same, basically for everything..

[dbrakenhoff]

Enforce dtypes, e.g. for names (=str). Check for illegal characters in strings.

[raoulcollenteur]

Closing after PR #415