Competition show user display name if available

[ihsaan-ullah]

@ mention of reviewers

@Didayolo

A brief description of the purpose of the changes contained in this PR.

1. Display Name

Now users can use display name instead of username in competitions

• Main page competitions show display name

• Competition detail page shows display name:

• Resources page: Task detail modal shows display name:

• Resources page: Dataset/program detail modal shows display name:

• Resources page: Submission detail modal shows display name:

• Server status page shows display name

• leaderboard already shows display name

2. Profile page

Profile page is retouched to show to the user his/her name, username, display name, email and some style change

Note: to other users, username, display name and email are not shown

Issues this PR resolves

• Use the display name for the organizer #1249

Checklist

• Code review by me
• Hand tested by me
• I'm proud of my work
• Code review by reviewer
• Hand tested by reviewer
• CircleCi tests are passing
• Ready to merge