Add/Refine templates for issues

Issues templates status:

• we have 2 (bug report and generic)
• there is a little bug in the label-adding part of (at least) the bug report one ("status" label needs quotation marks)
• they are not widely used

Possible improvements:

• set a default (so they are used more)
• fix the mentioned label bug
• add a template for sanitizer errors (as I tend to always make them look the same manually now)