Add base template for plain prints and optimize PDF generation

Necessary for AlekSIS-App-Kort

aleksis/core/static/print-simple.css

+@page {
+    padding: 0;
+    margin: 0;
+}
+
+/* Some stuff for tables */
+
+table.small-print, td.small-print, th.small-print {
+    font-size: 10pt;
+}
+
+tr {
+    border-bottom: 1px solid rgba(0, 0, 0, 0.3);
+}
+
+td, th {
+    padding: 1px;
+}
+
+td.rotate, th.rotate {
+    text-align: center;
+    transform: rotate(-90deg);
+}