ECDSA Support in signer (#1064)

* Add ecdsa support to signer

* Remove nix. Cleanup.

* remove ecdsa example and small tidy

* fmt

* fix wasm test

* feature flag ecdsa/sr25519 support, use global signing context

* clippy fix

* ensure signers all impl Signer trait in doc test

* fix CI

* fix digner test

* remove dead code warnings when no features enabled

* move dead code attr to right place

* fix random clippy error that popped up

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Co-authored-by: Lech Głowiak <lech.glowiak@gmail.com>

signer/src/crypto/seed_from_entropy.rs

@@ -10,6 +10,7 @@ use zeroize::Zeroize;
 /// This is taken from `substrate-bip39` so that we can keep dependencies in line, and
 /// is the same logic that sp-core uses to go from mnemonic entropy to seed. Returns
 /// `None` if invalid length.
+#[allow(dead_code)]
 pub fn seed_from_entropy(entropy: &[u8], password: &str) -> Option<[u8; 64]> {
     if entropy.len() < 16 || entropy.len() > 32 || entropy.len() % 4 != 0 {
         return None;