Fix compilation warnings

[vkomenda]

There are too many warning messages. Error messages drown in them and don't fit into the terminal buffer. Maybe some of them are fixed in v2.4.6, in which case a rebase onto v2.4.6 should be part of the fix. A few of the warnings are as follows:

  --> ethcore/src/miner/pool_client.rs:75:14
   |
75 |     engine: &'a EthEngine,
   |                 ^^^^^^^^^ help: use `dyn`: `dyn EthEngine`

warning: trait objects without an explicit `dyn` are deprecated
  --> ethcore/src/miner/pool_client.rs:76:16
   |
76 |     accounts: &'a LocalAccounts,
   |                   ^^^^^^^^^^^^^ help: use `dyn`: `dyn LocalAccounts`

warning: trait objects without an explicit `dyn` are deprecated
   --> ethcore/src/miner/pool_client.rs:101:15
    |
101 |         engine: &'a EthEngine,
    |                     ^^^^^^^^^ help: use `dyn`: `dyn EthEngine`

warning: trait objects without an explicit `dyn` are deprecated
   --> ethcore/src/miner/pool_client.rs:102:17
    |
102 |         accounts: &'a LocalAccounts,
    |                       ^^^^^^^^^^^^^ help: use `dyn`: `dyn LocalAccounts`

warning: trait objects without an explicit `dyn` are deprecated
  --> ethcore/src/pod_account.rs:82:43
   |
82 |     pub fn insert_additional(&self, db: &mut HashDB<KeccakHasher, DBValue>, factory: &TrieFactory<KeccakHasher, RlpCodec>) {
   |                                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use `dyn`: `dyn HashDB<KeccakHasher, DBValue>`