alias: default alias for all pages

[erwin]

When a new page is created, a default alias must be created based on the title of the page.

- special chars and spaces need to be stripped

- the alias must be unique so a check should be done

[erwin]

The default alias is set as follows: (build 35)

the default is set when the article (page news) is updated

• IF the alias was not already set
• and IF there is no published article for the current feed. (this is to remain backward compatible, we don't want url's of existing pages to change when they are updated)

The alias is equal to the title of the article, with only A-Za-Z0-9 characters. Other chars are stripped. Spaces are converted to underscores.