Add statistics and counter to Browser Assistant

[zzebrum]

Currently, AdGuard Browser Assistant does not display statistics on blocked ads.

The suggested features:

• a counter on the AdGuard Browser Assistant icon, as it is implemented in the AdGuard Browser Extension (the counter could replace letter 'A' on the icon)

Assistant icon

• statistics on blocked requests in the AdGuard Browser Assistant popup
• advanced statistics by types of blocked requests

AdGuard Browser Extension can be used for reference.

[zubrRB]

Duplicate of #25