Create TokenStaking contract

A token staking contract for a specified standard ERC20 token. A holder
of the specified token can stake its tokens to this contract and recover
the stake after undelegation period is over.

core/contracts/staking/TokenStaking.sol

@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: GPL-3.0-only
+
+pragma solidity ^0.8.9;
+
+/// @title TokenStaking
+/// @notice A token staking contract for a specified standard ERC20 token. A
+///         holder of the specified token can stake its tokens to this contract
+///         and recover the stake after undelegation period is over.
+contract TokenStaking {
+    // TODO: use IERC20 contract as type
+    address internal immutable token;
+
+    constructor(address _token) {
+        require(
+            address(_token) != address(0),
+            "Token can not be the zero address"
+        );
+
+        token = _token;
+    }
+}