Split up adminops

[alice-blue]

The "maintenance" heading on the adminops page includes links to these sections:

<h3>Maintenance</h3>
<ul>
    <li><a href="adminops?cleanpix">Delete orphaned images</a></li>
    <li><a href="adminops?reaper=30">Persistent session reaper</a></li>
    <li><a href="adminops?fixsortkeys">Fix NULL author/title sort keys in GAMES table</a></li>
    <li><a href="adminops?fixsortkeys&rebuild">Rebuild ALL author/title sort keys in GAMES table</a></li>
    <li><a href="adminops?rebuildgametags">Rebuild GAMES.TAGS from GAMETAGS contents</a></li>
    <li><a href="adminops?rebuildgametags2">Rebuild GAMETAGS from GAMES.TAGS</a></li>
    <li><a href="adminops?fixbafs">Fix &lt;A HREF&gt; tags in Baf's Guide reviews</a></li>
    <li><a href="adminops?filters">View/edit game filter list</a></li>
    <li><a href="adminops?utf8entities">Fix UTF-8 entities in database</a></li>
    <li><a href="adminops?sysinfo">Show server software versions</a></li>

This PR puts all of those linked "maintenance" sections of the adminops page--cleanpix, reaper, fixsortkeys, rebuildgametags, rebuildgametags2, fixbafs, filters, utf8entities, and sysinfo----in that order--into one new php file called "maintenance.php" My understanding is that these features are not often used, so it might help the adminops page to get these sections out of the way.

It'd be possible to include other sections in the maintenance page if we wanted to, but I thought I'd start here and see whether we want to go this way.

Also, this PR splits off "recent activity" into its own file, as it's a longish section.

Both of the new php files are in a new folder called adminops-components.