XWIKI-17421: Import code base from Mentions application

...ns-api/src/main/java/org/xwiki/mentions/DisplayStyle.java

...api/src/main/java/org/xwiki/mentions/MentionLocation.java

...n/java/org/xwiki/mentions/MentionNotificationService.java

...c/main/java/org/xwiki/mentions/MentionsConfiguration.java

...src/main/java/org/xwiki/mentions/events/MentionEvent.java

...in/java/org/xwiki/mentions/events/MentionEventParams.java

...java/org/xwiki/mentions/script/MentionsScriptService.java

...m-mentions-api/src/main/resources/META-INF/components.txt

.../mentions/internal/DefaultMentionNotificationService.java

...rg/xwiki/mentions/internal/DefaultMentionXDOMService.java

...xwiki/mentions/internal/DefaultMentionsConfiguration.java

.../java/org/xwiki/mentions/internal/MentionXDOMService.java

.../xwiki/mentions/internal/MentionsConfigurationSource.java

...xwiki/mentions/internal/async/MentionsCreatedRequest.java

.../xwiki/mentions/internal/async/MentionsCreatedStatus.java

...xwiki/mentions/internal/async/MentionsUpdatedRequest.java

.../xwiki/mentions/internal/async/MentionsUpdatedStatus.java

...xwiki/mentions/internal/async/jobs/MentionsCreateJob.java

...xwiki/mentions/internal/async/jobs/MentionsUpdateJob.java

...ions/internal/listeners/MentionsCreatedEventListener.java