Big refactor of multiple backends handling.

backend/src/api/bitcoin/electrum-api.interface.ts

@@ -0,0 +1,12 @@
+export namespace IElectrumApi {
+  export interface ScriptHashBalance {
+    confirmed: number;
+    unconfirmed: number;
+  }
+
+  export interface ScriptHashHistory {
+    height: number;
+    tx_hash: string;
+    fee?: number;
+  }
+}