Connection Switch with different Stacks-blockchain node

[gzelda]

Describe the bug
Now the Mining-bot could only connect with a fixed node IP address(now is krypton.blockstack.org, is written in service/constant.ts.
But the release version should allow user to use any node they want.

Expected behavior
The RightTop should have a switch list which contains a connection switch list, user can use official node, local node or cloud node.

[gzelda]

From the infrastructure of first version, each Mining-Bot will bind on a stacks-node. So this issue should be solved in beta version.