Create storage submodule http_api

Currently in the storage module we have a lot of qualified paths. We
can reduce the noise considerable by observing that the qualified
paths are all because of the load/save `http_api` types.

Create a submodule `http_api` of the storage module and confine to it
all of the load/save implementations for types defined in the main
`http_api` module.

cnd/src/db/tables.rs

@@ -1,5 +1,5 @@
 use crate::{
-    bitcoin,
+    asset, bitcoin,
     db::{
         schema::{address_book, halights, hbits, herc20s, secret_hashes, swaps},
         wrapper_types::{
@@ -146,6 +146,15 @@ impl IntoInsertable for herc20::CreatedSwap {
     }
 }
 
+impl From<Herc20> for asset::Erc20 {
+    fn from(herc20: Herc20) -> asset::Erc20 {
+        asset::Erc20 {
+            quantity: herc20.amount.0.into(),
+            token_contract: herc20.token_contract.0.into(),
+        }
+    }
+}
+
 #[derive(Associations, Clone, Debug, Identifiable, Queryable, PartialEq)]
 #[belongs_to(Swap)]
 #[table_name = "halights"]
@@ -201,6 +210,12 @@ impl IntoInsertable for halight::CreatedSwap {
     }
 }
 
+impl From<Halight> for asset::Bitcoin {
+    fn from(halight: Halight) -> Self {
+        halight.amount.0.into()
+    }
+}
+
 #[derive(Associations, Clone, Debug, Identifiable, Queryable, PartialEq)]
 #[belongs_to(Swap)]
 #[table_name = "hbits"]
@@ -244,6 +259,12 @@ impl IntoInsertable for hbit::CreatedSwap {
     }
 }
 
+impl From<Hbit> for asset::Bitcoin {
+    fn from(hbit: Hbit) -> Self {
+        hbit.amount.0.into()
+    }
+}
+
 impl Insert<InsertableHerc20> for Sqlite {
     fn insert(
         &self,