LUTECE-1832 : Allow the I18n cache to be reset

Introduce a resetCache method in I18nService and hook it up in the reset all cache feature.
This allows to change i18n messages at run time.
LUTECE-1835 : Initialize Lutece at context initialization time

Lutece initialization occurs before session de-passivation.
Merge pull request #6 from rzara/LUTECE-1835

LUTECE-1835 : Initialize Lutece at context initialization time
Merge pull request #4 from rzara/LUTECE-1832

LUTECE-1832 : Allow the I18n cache to be reset