[UI] Setup Routes

[pallabez]

• Install react router dom
• Setup route for / , /flag?mode=edit, /flag?mode=create

[akinsanmi60]

Kindly sign me up for further contributions

[Neha]

New requirements:

1.Add left nav #48
2. These would be in the left nav: users, segments, settings, env switching between test and prod
3. Other links on whole project: Create flag, edit, delete, login, logout