Add support for localized HTML

[mdouchin]

The upcoming version of the plugin will allow to use a new parameter to set the locale. See the PR https://github.com/3liz/qgis-pgmetadata-plugin/pull/50

In Lizmap module, we should

• get the current locale from jLocale
• test if this locale corresponds to one of the available locales. At present, $available_locales = array('en', 'fr');
• use the new version of the function SELECT pgmetadata.get_dataset_item_html_content('{schema}', '{table}', '{locale}'); with a try / catch (and use the old one if the first failed SELECT pgmetadata.get_dataset_item_html_content('{schema}', '{table}');

cc @drillinP @Gustry

[pdrillin]

Commits: a2405cbc4773da6369eebbf8bebc883fbc7cb52a, d643f921be7e78773c320eab991fbcd48c6d5e1b, 6984ecf44e4af6debc84d23ee56faf1bea001e53