Improve displaying of small/hard to spot annotations

[igoroctaviano]

Case: If clusters are not being used when number of annotations are less then 1000

• Update SLIM so when the user clicks in an annotation group (right panel), it zooms all to way to a random coordinate of that annotation group
• Improve annotations style so it scales better at lower resolutions making them easier to spot but not sure if this could confuse the pathologist (making them appear bigger than they are)