Node grouping and autoselection.

[Dexaran]

It is necessary to reorganize the node grouping and selection as it is done in MyCrypto.

• Node selection dropdown menu should be replaced with network selection dropdown menu.
• Network dropdown menu should contain network names. A user can select the network to which he wants to connect and then the wallet will go into the node auto-select mode. (it should ping the nodes of the chosen network and pick the better one to connect. It can be inherited from MyCrypto code)
• If a user wants to connect to a specified node of the chosen network, then he can open the dropdown menu of the selected network and pick the desired node.

[Dexaran]

There is no need to implement the "other networks" button. We can just list all supported networks in the "network menu".