Refactor triedb constructors to error on invalid state root (#1230)

* add TrieError, refactor Trie DB creation

* remove Result type alias due to glob import conflicts

* fix fallout in state.rs

* add debug, display impl for TrieError

* fix fallout in account.rs

* ethcore::Error::TrieError variant

* fix remaining fallout in ethcore crate

* added From<TrieError> impl for Error, removed map_err calls

* fix test breakages

* fix doc tests

* update docs

[ci skip]