Optimize offset scoring and corresponding information on the server pages

[daerSeebaer]

This issue tracks the current adjustments to the monitoring in regards to time offset.

Changes to the offset thresholds

• Historic issue: Make the scoring algorithm harsher #145
• Discussion about tolerated offset
• Decide on the following thresholds:
  • When does point deduction start (old value: 75ms)
  • When is a server considered non viable for the pool (old value: 125ms)
• Change offset scoring in the monitoring

Changes to the way the information is presented on the pool website

• Make server page graph coloring consistent with scoring #249
• Parametrize the number in the graph_explanation section
• Enter the new threshold value(s)