Rework/Improve the Slurmdbd related API

[tazend]

General

• [ ] Put into seperate package: slurmdbd
• [ ] Have a central class to manage opening/closing Slurmdbd connections

Portions that need a rework or new/improved Functionality

• [ ] Implement handling Users/Accounts/Associations (List/Modify/Delete/Add)
• [ ] Implement handling WCKeys (List/Modify/Delete/Add)
• [ ] Improve listing Events
• [ ] Improve listing Transactions
• [ ] Improve listing Reservations
• [ ] Improve/Implement Cluster functions (List/Modify/Delete/Add)
• [ ] Improve/Implement QOS functions (List/Modify/Delete/Add)
• [ ] Implement fetching slurmdbd config
• [ ] Implement Archive functionality
• [ ] Implement listing TRES
• [ ] Implement listing Runaway Jobs