Added SampleToken ERC20

Course_Identity_And_Smart_Contracts/SampleToken/contracts/Migrations.sol

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+pragma solidity >=0.4.21 <0.6.0;
+
+contract Migrations {
+  address public owner;
+  uint public last_completed_migration;
+
+  constructor() public {
+    owner = msg.sender;
+  }
+
+  modifier restricted() {
+    if (msg.sender == owner) _;
+  }
+
+  function setCompleted(uint completed) public restricted {
+    last_completed_migration = completed;
+  }
+
+  function upgrade(address new_address) public restricted {
+    Migrations upgraded = Migrations(new_address);
+    upgraded.setCompleted(last_completed_migration);
+  }
+}

Course_Identity_And_Smart_Contracts/SampleToken/contracts/SampleToken.sol

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+pragma solidity >=0.4.24;
+
+import "../node_modules/openzeppelin-solidity/contracts/token/ERC20/ERC20.sol";
+import "../node_modules/openzeppelin-solidity/contracts/token/ERC20/ERC20Detailed.sol";
+
+contract SampleToken is ERC20Detailed, ERC20 {
+
+    constructor(string memory _name, string memory _symbol, uint8 _decimals, uint _initialSupply) 
+    ERC20Detailed(_name, _symbol, _decimals) public {
+        require(_initialSupply > 0, "INITIAL_SUPPLY has to be greater than 0");
+        _mint(msg.sender, _initialSupply);
+    }
+}

Course_Identity_And_Smart_Contracts/SampleToken/migrations/1_initial_migration.js

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+var Migrations = artifacts.require("./Migrations.sol");
+
+module.exports = function(deployer) {
+  deployer.deploy(Migrations);
+};

Course_Identity_And_Smart_Contracts/SampleToken/migrations/2_initial_migration.js

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+var SampleToken = artifacts.require("SampleToken");
+
+module.exports = function(deployer) {
+  deployer.deploy(SampleToken, "UdacityExampleToken", "UET", 18, 1000);
+};