Add collect filter to template renderer.

This filter can collect attributes from items having the
same key into a single item.

Can be used in templates like this:

{% for Entry in Sequence.Entries |
   collect("ShotPointId", ["EntryType", "Comment"]) %}

to avoid duplicating shotpoint numbers.

lib/www/server/lib/render.js

@@ -13,6 +13,22 @@ function njkFind (ary, key, value) {
 	}
 }
 
+function njkCollect (entries, key, collectables) {
+	const out = [];
+	for (const entry of entries) {
+		if (out.find(i => i[key] == entry[key])) {
+			continue;
+		}
+		const others = entries.filter(item => item[key] == entry[key]);
+		const obj = Object.assign({}, entry);
+		for (const collectable of collectables) {
+			obj[collectable] = others.map(i => i[collectable]).filter(i => typeof i !== "undefined" && i !== "");
+		}
+		out.push(obj);
+	}
+	return out;
+}
+
 function njkPadStart (str, len, chr) {
 	return String(str).padStart(len, chr);
 }
@@ -42,6 +58,7 @@ async function render (data, template) {
 	
 	const nenv = nunjucks.configure(Path.dirname(template), {autoescape: false, lstripBlocks: false, trimBlocks: false});
 	nenv.addFilter('find', njkFind);
+	nenv.addFilter('collect', njkCollect);
 	nenv.addFilter('padStart', njkPadStart);
 	nenv.addFilter('timestamp', njkTimestamp);
 	nenv.addFilter('markdown', njkMarkdown);