Added search bar in Django Admin Users and competitions pages as well as some filters

[ObadaS]

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

Added search bar in Django Admin Users and competitions pages as well as some filters

Checklist

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