Useful Quickfixes that are missing

[jthoene]

• msg.gas -> gasleft() : msg.gas has been deprecated in favor of gasleft()
• change type "address" of variable to "address payable" if the "send" or "transfer" function is used for this variable: "send" and "transfer" are only available for objects of type "address payable", not "address".
• make function payable for the following compiler error: "msg.value" and "callvalue()" can only be used in payable public functions. Make the function "payable" or use an internal function to avoid this error.
• Add datalocation for return parameters: Data location must be "memory" or "calldata" for return parameter in function, but none was given.
• Add datalocation for variables: Data location must be "storage", "memory" or "calldata" for variable, but none was given. - Change "block.blockhash()" to "blockhash()": "block.blockhash()" has been deprecated in favor of "blockhash()"
• Make contract abstract: Contract "xxxx" should be marked as abstract.
• Mark function as virtual: Functions without implementation must be marked virtual.
• Add override keyword for functions, which override a method: Overriding function is missing "override" specifier.