Replace DP "is_alive" check with a BAC; change link to POST

[prioux]

The page that allows an admin to trigger a set of live 'is_alive?' checks on the DPs, from the perspective of any portal or bourreaux, has two issues.

1. the link to trigger a refresh of the table is done with GET requests instead of POST
2. the code that is triggered is a loop within the old spawn_with_active_records() utility, which should be replaced by a BackgroundActivity object instead.

[MontrealSergiy]

@prioux

should I allow normal user update the dataprovider status?

[prioux]

@MontrealSergiy No, let this be an admin only feature, since it's expensive