new client various fixes: flagging; non-Public Challenges can have 0 gem prize; etc (#9072)

* allow a user (admin or non-admin) to flag their own message

Initially implemented in https://github.com/HabitRPG/habitica/issues/8005

Use case for a non-admin needing to flag their own message:
- a new user posts a question
- a socialite answers
- the user posts again and reveals that they're under 13
- the socialite flags all of the user's messages and all replies to the user including the socialite's own reply (it's a requirement that all messages to and from under-aged users be hidden and some socialites know this)

* change NPC message for Tavern: "Rest in the Inn" > "Pause Damage"

* prevent a chat message being hidden until it's been flagged more than once

* allow non-Tavern (non-"Public") challenges to have zero gem prize

Also changes message about gem prize to say "Public Challenges" instead of "Tavern Challenges"

* finish committing merge conflict

website/client/components/challenges/challengeModal.vue

@@ -300,16 +300,8 @@ export default {
       return userBalance + groupBalance;
     },
     minPrize () {
-      let groupFound;
-      this.groups.forEach(group => {
-        if (group._id === this.workingChallenge.group) {
-          groupFound = group;
-          return;
-        }
-      });
-
-      if (groupFound && groupFound.privacy === 'private') return 0;
-      return 1;
+      if (this.workingChallenge.group === TAVERN_ID) return 1;
+      return 0;
     },
     insufficientGemsForTavernChallenge () {
       let balance = this.user.balance || 0;