Move virtual ops to plugins

[theoreticalbts]

It seems like it would be useful to have plugins able to create v-ops, and re-work existing core v-ops into plugins. Then if we upgrade v-ops in any way, clients can use their configuration to choose what v-ops are generated and whether they break operation history. This approach loses consistent numbering of op history and gives everybody different v-op set based on their configuration -- but that is OK. V-ops and operation history are inherently things which are used by particular UI implementations and are not core features. Related: #246 #570

[vikramrajkumar]

This issue was moved to bitshares/bitshares-core#157