Basic users and groups manager UI

Issue #14

Completed tasks:
1. Sidebar for completed for users and groups.
2. Displaying users and help content.
3. User add modal window.
Volume-raid UI.

Issue #13

This commit includes fixes for below issues:
1. Clearing previous setTimeout callback events.
2. Stop polling when switches to different module.
3. Corrected indentation to 4 spaces.