NXD Show "about" footer on every page

We show in small font size the same info that is shown on sign_in page:

    "GitLab Nexedi Edition", "About GitLab" and "About Nexedi"

This is good to have and hereby-introduced about-footer area will be
also used in the next patch for ICP too.

XXX placement of .about-footer to be near bottom is done not very
correctly.

app/assets/stylesheets/framework/sidebar.scss

 .content-wrapper {
   width: 100%;
+  // XXX hack for .about-footer to be near bottom, if not enough content in .container-fluid
+  min-height: 85vh;
 
   .container-fluid {
     padding: 0 $gl-padding;
@@ -16,6 +18,17 @@
   transition: padding $sidebar-transition-duration;
 }
 
+.about-footer {
+  text-align: center;
+  padding: 10px;
+  padding-top: 14px; // increased: e.g. new_note form can overlap with only 10px top padding
+  a {
+    margin-left:  3px;
+    margin-right: 3px;
+  }
+  font-size: small
+}
+
 .nav-header-btn {
   padding: 10px $gl-sidebar-padding;
   color: inherit;

app/views/layouts/_page.html.haml

@@ -27,3 +27,9 @@
         = render "layouts/flash", extra_flash_class: 'limit-container-width'
         = yield :before_content
         = yield
+  .about-footer
+    = link_to "GitLab Nexedi Edition", "https://lab.nexedi.com/nexedi/slapos/blob/master/software/gitlab/software.cfg"
+    |
+    = link_to "About GitLab", "https://about.gitlab.com/"
+    |
+    = link_to "About Nexedi", "http://www.nexedi.com/"