Make changes in response to beta feedback

[tsmith023]

• Introduce collections.use() in place of collections.get() deprecating the latter may come in subsequent RC
• Fix bug when updating legacy vectorizer's index configuration
• Split vectorizer into vectorizer and vectorizers in collections.create()
• Deprecate vectorizer with a warning in favour of vectorizers
• Allow vectorizers to accept instance of NamedVectorizerConfig
• Refactors configure.namedVectorizer() method into separate individual methods within configure.namedVectorizer. namespace for each vectorizer
• Renames all instances of namedVectorizer to vectorizer thereby forbidding legacy vectorization for new collections
• Renames all instances of vectorizeClassName to vectorizeCollectionName
• Adds specific errors as class extensions of Error for certain failure modes, e.g. WeaviateQueryError