You are probably talking of a mechanism specific to some bitcoin wallets. Any modification of the data of the blockchain needs to be done in transactions which are mined. Thats the very basis of the blockchain security. If you think my answer is correct please mark this answer as accepted, thank you :)

What do you call an internal transaction ?

As long as you use ethereum accounts for your users and in your smart contract you check access based on msg.sender, the security is guaranteed by the network, and is probably much better that a traditional web apps with user/password

Ok. Lets make sure we understand each other well for the 2nd question. When you say "its contract", what do you mean? A node does not possess any contract. And when you say "who send the transaction", do you mean the ethereum account or something else ?

Sounds like its a required file by truffle itself, which is supposed to be located in truffle dir. Try to reinstall a fresh version of truffle

Im not quite sure what you mean by "a transaction come from a real device", but all I can tell you is that its not something the blockchain will provide you, so you need to handle this outside the blockchain

i mean the grep command line utility that allow you to search into multiple files.

Can you do a grep on Migrations.sol on your whole project? You will see where you reference this contract

Can you copy paste the content of your migration file ?