Rename EnvTypes -> Env (and many other renamings) (#513)

* [env] rename Env -> EnvBackend, TypedEnv -> TypedEnvBackend

* [env] rename EnvError -> Error

* [*] rename ink_env::EnvTypes -> Environment

Namely rename:
ink_env::EnvTypes -> Environment
ink_env::DefaultEnvTypes -> DefaultEnvironment

* [*] update cfg-if dependency 0.1 -> 1.0

* [alloc] rename ink_alloc -> ink_allocator

* [env] forgot to rename in lib.rs

* [env, lang] fix some bugs with ink_env::EnvError -> Error renaming

* [ci] adjust renaming of ink_alloc -> ink_allocator

* [env] apply rustfmt

* [lang/macro] re-enable disabled UI test

* [examples] DNS: apply rustfmt

* [examples] ERC-20, ERC-721: apply rustfmt
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