api: add pagination for guilds

start adding apiMessages

add apiMessages lib with tests

use apiMessage and fix tests

fix content tests

guilds pagination: add api docs

guilds pagination: improve api docs

website/server/libs/apiMessages.js

@@ -0,0 +1,21 @@
+// A map of messages used by the API that don't need to be translated and
+// so are not placed into /common/locales
+
+import _ from 'lodash';
+
+// When this file grows, it can be split into multiple ones.
+const messages = {
+  guildsOnlyPaginate: 'Only public guilds support pagination.',
+  guildsPaginateBooleanString: 'req.query.paginate must be a boolean string.',
+  guildsPageInteger: 'req.query.page must be an integer greater than or equal to 0.',
+};
+
+export default function (msgKey, vars = {}) {
+  let message = messages[msgKey];
+  if (!message) throw new Error(`Error processing the API message "${msgKey}".`);
+
+  let clonedVars = vars ? _.clone(vars) : {};
+
+  // TODO cache the result of template() ? More memory usage, faster output
+  return _.template(message)(clonedVars);
+}