Implement a new indexing_type and category for forums

[m-i-l]

At the moment there are a few forums indexed under the "independent sites" category. However, the way the spidering works (50 pages max, only fully indexed once a month), they aren't likely to produce many useful search results. Many of the forums will have APIs / data feeds though, so it should be possible to index them more efficiently than the current spider.

searchmysite.net does have a field for indexing_type - currently every site is "spider/default" (although there was a feed/wikipedia at one point), so there could be an other type like "feed/forum" (maybe later even more specific ones like "feed/phpbb"), and the appropriate code to support that.

There could even be a 3rd category on the Add Site page ("Personal website", "Independent website" and "Forum") which would automatically set indexing_type to "feed/forum".

Existing submissions would need to be reviewed and changed to the new indexing_type and category if necessary as part of this change.

As an aside, the original idea had been that people would set up different searchmysite.net instances to focus on different parts of the internet, with the view that someone might set up an instance dedicated to searching forums (a bit like community driven versions of https://boardreader.com/ , https://crowdview.ai/ etc.). This change wouldn't prevent that - in fact it would make it easier if all the forum-specific indexing code was already implemented.