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

node/specs/gtest_client-specs.json

+{
+    "name": "ĞTest",
+    "id": "gtest",
+    "chainType": "Live",
+    "bootNodes": [],
+    "telemetryEndpoints": [
+        [
+            "/dns/telemetry.polkadot.io/tcp/443/x-parity-wss/%2Fsubmit%2F",
+            0
+        ]
+    ],
+    "properties": {
+        "tokenDecimals": 2,
+        "tokenSymbol": "ĞT"
+    }
+}
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