Small change to Argon template

I added an option to the nice Argon dokuwiki template to get rid of the left sidebar for users that have not logged in so that the entire width of the page can be used for text. Here are the changes I made:

Changes to main.php (in lib/tpl/argon/)

Top of the file, below original line 10, add the line:

$showLeftSidebar = !tpl_getConf('hideLeftSidebar') || !empty($_SERVER['REMOTE_USER']);

Below line 133 (original line 132, after the left sidebar comment), add the line:
```
<?php if ($showLeftSidebar) { ?>
```

Around line 198, after the code

<!-- center content -->
<main class="col-12 col-md-9 col-xl-8 py-md-3 pl-md-5 ct-content dokuwiki" role="main">

add the following three lines:

<?php } else { ?>
<main class="col-12 col-md-115 col-xl-10 py-md-3 pl-md-5 ct-content dokuwiki" role="main">                  
<?php }?>

Changes to default.php (in lib/tpl/argon/conf/)
- Add:
```
$conf['hideLeftSidebar']  = 0;
```

Changes to meta.php (in lib/tpl/argon/conf/)

Add:

$meta['hideLeftSidebar']  = array('onoff');

Changes to doku.css (in lib/tpl/argon/assets/css/doku.css)

Update line 657 from

.col-md-auto, .col-md-12, .col-md-11, .col-md-10, .col-md-9, .col-md-8, .col-md-7, .col-md-6, .col-md-5, .col-md-4, .col-md-3, .col-md-2, .col-md-1, .col-sm,

to

.col-md-auto, .col-md-12, .col-md-115, .col-md-11, .col-md-10, .col-md-9, .col-md-8, .col-md-7, .col-md-6, .col-md-5, .col-md-4, .col-md-3, .col-md-2, .col-md-1, .col-sm,

Add

.col-md-115 {
flex: 0 0 97.5%;
max-width: 97.5%;
}

after line 1183 (after the closing brace).

Changes to settings.php (in lib/tpl/argon/lang/en/settings.php)
- Add:
```
$lang['hideLeftSidebar']  = 'Hide left sidebar when not logged in?';
```
- Similar changes should be made for other languages as well.

With these changes, a new option should appear in the template configuration settings that allows you to turn off the left sidebar.