Generate different pages for different locales 

Hi,

This pull request adds the possibility to generate several sets of pages in different languages.
They are saved in:
`html/<locale_langcode>/`
and can be served as:
`<wtosm_root>/<locale_langcode>/`

In the directory `html/img/lang`there are flags for locales (taken from Wikimedia Commons:[Project Nuvola 2.0+/Flags](https://commons.wikimedia.org/wiki/Commons:Project_Nuvola_2.0%2B/Flags)) to add more flags just save them as `<locale_langcode>.svg`.

Cheers,

Cristian