Change reference to Tokens documentation
Fix typo `CROWDALE_ADDRESS` to `CROWDSALE_ADDRESS`

Resolve compilation errors in sample contracts:
* Change `address wallet` to `address payable wallet` in multiple sample contracts
* Change `ERC20 token` to `IERC20 token` in multiple sample contracts
* Reorder inheritance of crowdsales to prevent error: "Linearization of inheritance graph impossible" in multiple sample contracts
* Change `startTime` to constructor parameter `openingTime`