add summary field to challenges and guilds (#8960)

* create new summary field for challenges

* finish implementating summary for challenges, add some support for guilds

* make small improvements to challenges code

* fix lint errors

* add more code to support summaries for guilds (still more needed)

* fix existing tests by adding summary field

* make existing tests pass

* WIP make "Public Challenges" text translatable

* change "leader" locale key to "guildOrPartyLeader" to make searches for it easier

* remove v-once from h2 headings

* remove failed attempt to localise text in <script>

* add quick-and-dirty error checking for guild not having categories

* make "Public Challenges" text translatable

* rename final ...PlaceHolder strings to ...Placeholder (lower-case "h") for consistency with existing Placeholder strings

test/api/v3/integration/challenges/GET-challenges_challengeId.test.js

@@ -50,6 +50,7 @@ describe('GET /challenges/:challengeId', () => {
         _id: group._id,
         id: group.id,
         name: group.name,
+        summary: group.name,
         type: group.type,
         privacy: group.privacy,
         leader: groupLeader.id,
@@ -102,6 +103,7 @@ describe('GET /challenges/:challengeId', () => {
         _id: group._id,
         id: group.id,
         name: group.name,
+        summary: group.name,
         type: group.type,
         privacy: group.privacy,
         leader: groupLeader.id,
@@ -154,6 +156,7 @@ describe('GET /challenges/:challengeId', () => {
         _id: group._id,
         id: group.id,
         name: group.name,
+        summary: group.name,
         type: group.type,
         privacy: group.privacy,
         leader: groupLeader.id,