stats: main page statistics migration

[bragov4ik]

• Adapt calculation of the correspoding charts from main page/txns page/verified contracts page stats: prepare counters for main page #1080
• Create a separate handle(-s) for the frontend to query (to not show duplicate data on the main /stats page) stats: separate handle(-s) for some page stats #1149
  • Allow configuring charts between handles (or hard-code in probuf?)
• Add support for multi-stage (dynamic) chart update start stats: delayed start of initialization of some charts #1102