[Feature Request] add search filters and an administrator to customize them

[ghost]

• I carefully read the contribution guidelines and agree to them.
• I checked if the issue/feature exists in the latest version.

I see that there are many videos that have sexual or violent content for adults that is not filtered with the option to "disable content restricted by age".
I would add a filter manager, to determine which words should not be received as a title results or when searching with those words.

[pavanvo]

On PeerTube +18 adults videos still showing in video's line with the option "disable content restricted by age".
But with this option this videos is not possible to watch.

I guess need to add one more check

for each video
   if  video marked as +18
       do not put them to line (search result)