Add ability to dump and restore state counter from persistent database (shelve)

[sshishov]

When use persistent=True to dump state to the file, counter data is not dumped.

Therefore after restoring from the file, on dashboard we do not see any statistics, everything is 0.

To add ability to store counter along with the state, __reduce__ method was overridden and __init__ to accept counter.

Note: we can try to restore from kwargs but for these we need to create __new__ constructor for EventState class and add additional magic method (as shelve is using protocol 3 by default)

[sshishov]

Fixes #787 partially (dashboard issue)

[rmk135]

I hope this get merged once

[rmk135]

@mher , please, merge this.

[SardarDelha]

merge this

[sshishov]

Very soon it will be anniverasy of 5 years 🎉