(Feature) Add support for the Kovan testnet

[varasev]

• (Mandatory) Description These changes add support for the Kovan network. UI colors and logo have been copied from Sokol styles.

• (Mandatory) What is it: (Fix), (Feature), or (Refactor) in Title (Feature)

[varasev]

There are no ballots yet, of course, so the main page is empty:

[varasev]

Done for Voting DApp:

[varasev]

@pashagonchar Please make a new logo for Kovan for the Governance App: https://github.com/varasev/poa-dapps-voting/blob/kovan-network/src/components/LogoKovan/logo.svg

And for the loading screen: https://github.com/varasev/poa-dapps-voting/blob/kovan-network/src/components/Loading/kovan.svg

[pashagonchar]

@varasev kovan_governance_logo.zip kovan_loader.svg.zip