Add Clean action for delayed queue

Add a Clean action for the queue in delayed status.
Ref. #18

thanks @alexleroyross for your first contribution to the project!

Fix missing total_system_memory data

Fix issue when total_system_memory is not present

Ref #12

Thanks @daksamit @sjsn for reporting the bug and help understanding the problem!

Visual improvements for highlighting

• Queue data and error stack traces with better highlighting

First complete working version

First working version with correct dependencies in place and minimal features available to users

• Auto polls status for each queue.
• Retry one or all failed jobs
• Status overview for queue healthy (such as memory and connected clients)