Documentation: update docs, screenshots ahead of Paperless-ngx v2.0 (#4542)

* Reformat internal links

* Update screenshots, docs & readme

* Use image lightbox

* Fix nested list on docs index

* Add some visual interest to screenshots layout

* Compress images

docs/assets/extra.css

@@ -20,6 +20,28 @@
         margin-left: 4%;
         float: left;
     }
+
+    .grid-flipped-left {
+        width: 66%;
+        float: left;
+    }
+
+    .grid-flipped-right {
+        width: 29%;
+        margin-left: 4%;
+        float: left;
+    }
+
+    .grid-half-left {
+        width: 48%;
+        float: left;
+    }
+
+    .grid-half-right {
+        width: 48%;
+        margin-left: 4%;
+        float: left;
+    }
 }
 
 .grid-left > p {
@@ -31,6 +53,12 @@
     margin: 0;
 }
 
+.clear {
+    clear: both;
+    margin-bottom: 20px;
+    display: block;
+}
+
 .index-callout {
     margin-right: .5rem;
 }