Feature: Refactor and fix the Language filter method

[syphax-bouazzouni]

Context

This PR does a global rewrite and refactor of all the work done in the Multilingual topic with the PRs listed bellow

• https://github.com/ontoportal-lirmm/goo/pull/40
• https://github.com/ontoportal-lirmm/goo/pull/39
• https://github.com/ontoportal-lirmm/goo/pull/38
• https://github.com/ontoportal-lirmm/goo/pull/37
• https://github.com/ontoportal-lirmm/goo/pull/32
• https://github.com/ontoportal-lirmm/goo/pull/24

Changes

• Give better names to the methods
• Remove unused methods and variables
• Limit the coupling between the two modules of SolutionMapper and LangFilter;
• Replace the getters argument to show languages from :show_all_languages to show_languages: true (https://github.com/ontoportal-lirmm/goo/pull/41/commits/e26009af8a11ffbc6a7ab016c41645b76bcac936)
• Fix save_model_values method to not save RDF:Literal object but a string (https://github.com/ontoportal-lirmm/goo/pull/41/commits/a990260bdea958ce293c1de75234ee0c25fb9213)
• Fix getters for list attributes to not take only the first value (https://github.com/ontoportal-lirmm/goo/pull/41/commits/94959cd3c34c2d7d6fa27b9220aa908d67114cd3)