core, subkey: allow to read Polkadot, Kusama, and Dothereum address types (#3643)

* core/primitives: set dothereum address type to 4

* subkey: add dothereum to network prefix

* core/primitives: set dothereum address type to 20

* core/primitives: update comment

* core/primitives: set default address to Dothereum

* Revert "core/primitives: set default address to Dothereum"

This reverts commit 2fc95490c89390eb26f200cb314435b1e9ff83e8.

* core/primitives: allow to parse different default address types