Development for Marseille/DREAL project.

Everything specific to the project (files under otp-analyst-client/src/main/webapp/marseille) are probably not meant to be merged.

Content:
- TimeGrid as simple PNG
- OTPA JavaScript/leaflet library to display gradient layer, legends, standard request parameters
- Various small fixes on isoline / grid sampling
- i18n of legacy JS analyst client with French translations

There should not be many impact on existing code as those changes are mainly new development.