Add a memory information in the status bar

Adds a progress bar in the status bar displaying the memory status of the server being the most used (in %). This is close to what is displayed in the Memory Inspector but is intended to be more visible, to help the user see when a server has a high load.

The progress bar has a different color depending on the load:

• load < 75%:
  • 
• 75% <= load < 90%:
  • 
• 90% <= load:
  •