ui/SectionList component (#4292)

* array chunking utility

* add SectionList component

* Add TODOs to indicate possible future work

* Add missing overlay style (as used in dapps at present)

js/src/ui/SectionList/sectionList.css

@@ -0,0 +1,72 @@
+/* Copyright 2015, 2016 Parity Technologies (UK) Ltd.
+/* This file is part of Parity.
+/*
+/* Parity is free software: you can redistribute it and/or modify
+/* it under the terms of the GNU General Public License as published by
+/* the Free Software Foundation, either version 3 of the License, or
+/* (at your option) any later version.
+/*
+/* Parity is distributed in the hope that it will be useful,
+/* but WITHOUT ANY WARRANTY; without even the implied warranty of
+/* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+/* GNU General Public License for more details.
+/*
+/* You should have received a copy of the GNU General Public License
+/* along with Parity.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+.section {
+  margin-bottom: 1em;
+  position: relative;
+
+  .overlay {
+    background: rgba(0, 0, 0, 0.85);
+    bottom: 0;
+    left: 0;
+    padding: 1.5em;
+    position: absolute;
+    right: 0;
+    top: 0;
+    z-index: 199;
+  }
+
+  .row {
+    display: flex;
+    justify-content: center;
+
+    /* TODO: As per JS comments, the flex-base could be adjusted in the future to allow for */
+    /* case where <> 3 columns are required should the need arrise from a UI pov. */
+    .item {
+      box-sizing: border-box;
+      cursor: pointer;
+      flex: 0 1 33.33%;
+      height: 100%;
+      opacity: 0.75;
+      padding: 0.25em;
+      transition: all 0.75s cubic-bezier(0.23, 1, 0.32, 1);
+
+      /* TODO: The hover and no-hover states can be improved to not "just appear" */
+      &:not(:hover) {
+        & [data-hover="hide"] {
+        }
+
+        & [data-hover="show"] {
+          display: none;
+        }
+      }
+
+      &:hover {
+        flex: 0 0 50%;
+        opacity: 1;
+        z-index: 100;
+
+        & [data-hover="hide"] {
+          display: none;
+        }
+
+        & [data-hover="show"] {
+        }
+      }
+    }
+  }
+}