Add automated Sitemap creation

[tramuntanal]

🎩 What? Why?

• Add a rake task to generate a sitemap.xml and a serie of sub-sitemaps.
• Add a whenever schedule for: every 1.day, at: "3:15 am"
• Implement tests

📷 Screenshots (optional)

$ bin/rails sitemap:generate
Sitemap generation is intended for production environments only. Forced.
In '...public/':
+ sitemaps/processes.xml.gz                              137 links /    2.29 KB
+ sitemaps/regulations.xml.gz                            228 links /    3.23 KB
+ sitemaps/assemblies.xml.gz                             107 links /    2.06 KB
+ sitemaps/meetings.xml.gz                                70 links /    1.25 KB
+ sitemaps/proposals.xml.gz                             3323 links /    15.7 KB
+ sitemaps/pages.xml.gz                                   17 links /  631 Bytes
+ sitemaps/blogs.xml.gz                                    6 links /  488 Bytes
+ sitemaps/debates.xml.gz                                 13 links /  657 Bytes
+ sitemaps/budgets.xml.gz                                 23 links /  624 Bytes
+ sitemaps/accountability.xml.gz                          10 links /  575 Bytes
+ sitemaps/attachments.xml.gz                            538 links /    21.8 KB
+ sitemaps/sitemap.xml.gz                              11 sitemaps /  352 Bytes
Sitemap stats: 4,472 links / 11 sitemaps / 0m02s
robots.txt updated with 12 Sitemap directives.