i18n: add AOT config, messages fr-en files, and core functionnality.

webapp/README.md

webapp/package.json

webapp/src/app/core/components/footer/footer.component.html

webapp/src/app/core/components/header/header.component.html

...ts/filter-list/filter-detail/filter-detail.component.html

...ents/filter-list/filter-detail/filter-detail.component.ts

...p/src/app/geosource/models/elasticsearch-options.model.ts

webapp/src/app/geosource/models/filter.model.ts

webapp/src/locale/messages.en.xlf

webapp/src/locale/messages.fr.xlf