Better 404 (and 403) pages

Fixes #1819

static/img/40x/QE-logomark.svg

@@ -0,0 +1 @@
+<svg id="Layer_1" data-name="Layer 1" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 203.92 187.45"><defs><style>.cls-1{fill:#05ce7c;}.cls-2{fill:#003764;}</style></defs><title>Artboard 1</title><polygon class="cls-1" points="159.61 0 203.92 93.72 159.61 187.45 121.89 187.45 166.2 93.72 121.89 0 159.61 0"/><polygon class="cls-2" points="121.9 187.45 77.59 93.72 121.9 0 159.62 0 115.31 93.72 159.62 187.45 121.9 187.45"/><polygon class="cls-1" points="101.96 42.17 82.02 0 44.3 0 83.1 82.06 101.96 42.17"/><polygon class="cls-1" points="83.1 105.38 44.3 187.45 82.02 187.45 101.96 145.27 83.1 105.38"/><polygon class="cls-2" points="44.31 187.45 0 93.72 44.31 0 82.03 0 37.72 93.72 82.03 187.45 44.31 187.45"/></svg>

static/img/40x/Quay-logomark.svg

@@ -0,0 +1 @@
+<svg id="Layer_1" data-name="Layer 1" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 204 187.48"><defs><style>.cls-1{fill:#40b4e5;}.cls-2{fill:#003764;}</style></defs><title>Artboard 1</title><polygon class="cls-1" points="159.68 -0.04 204 93.72 159.68 187.48 121.94 187.48 166.27 93.72 121.94 -0.04 159.68 -0.04"/><polygon class="cls-2" points="121.94 187.48 77.62 93.72 121.94 -0.04 159.68 -0.04 115.35 93.72 159.68 187.48 121.94 187.48"/><polygon class="cls-1" points="102 42.15 82.06 -0.04 44.32 -0.04 83.13 82.06 102 42.15"/><polygon class="cls-1" points="83.13 105.39 44.32 187.48 82.06 187.48 102 145.29 83.13 105.39"/><polygon class="cls-2" points="44.33 187.48 0 93.72 44.33 -0.04 82.06 -0.04 37.73 93.72 82.06 187.48 44.33 187.48"/></svg>