Fix the Communities menu CSS positioning in the plugin

[tanius]

The recent version of Discourse that we installed on our multisite Discourse instance on 2019-09-30 introduced some template change that makes our current Communities menu CSS (and similarly, that of all menu items in our custom menu bar) no longer applicable. Namely, these menu items will take space away from the main content width, which is mostly noticeable in mobile mode (and only when directly visiting a topic or reloading after visiting a topic).

The best fix seems to be position: absolute on the whole menu bar, taking it out of the usual HTML content flow:

.edgeryders_communities_navigation {
    position: absolute;
    width: 100%;
}

#main-outlet {
    /* Move all page content down by the 30px that an absolutely positioned 
       navbar takes up at the top. */
    padding-top: calc(5.8572em + 30px);
}

nav#bar .wrap {
    position: initial;
}

That fix has been applied on all our sites (multisite instance sites plus edgeryders.eu) via the theme customization admin backend feature already. It now has to be moved to our Communities Navigation plugin. Doing so only needs the first two CSS rule from above, plus removing nav#bar .wrap { position: relative; } which is defined in the plugin right now.