gtest genesis parsing

• only embed chainspec when feature enabled
• change existential deposit to match g1v1
• adapt genesis parsing to real-world data

# build with gtest feature
cargo build --release --features gtest --no-default-features
# run with custom genesis
DUNITER_GTEST_GENESIS=~/dev/py-g1-migrator/output/gtest_genesis.json duniter --tmp --alice --chain=gtest_dev

pallets/identity/src/lib.rs

@@ -157,7 +157,7 @@ pub mod pallet {
             identities.sort_unstable_by(|a, b| a.index.cmp(&b.index));
 
             for idty in identities.into_iter() {
-                let idty_index = Pallet::<T>::get_next_idty_index();
+                let idty_index = idty.index;
                 if idty.value.removable_on > T::BlockNumber::zero() {
                     <IdentitiesRemovableOn<T>>::append(
                         idty.value.removable_on,