Display "last modified time" of bitcoin.conf in splash screen #76

Is your feature request related to a problem? Please describe.

• bitcoin.conf file is used by lot of users with different settings
• any malware can modify this file which can affect bitcoin core wallet
• if the user is unaware of changes made by someone else in bitcoin.conf, it may affect UX, privacy and maybe security

Describe the solution you'd like

• user should be notified if the file was changed when wallet is loading

Describe alternatives you've considered

• maybe user can keep his system secure and bitcoin core related files however the solution I suggested is basic information about file modification time and changes nothing much related to how wallet works

Additional context Maybe we can add text below "The Bitcoin Core Developers" to display such information

I discussed the issue here: https://bitcoin.stackexchange.com/questions/98727/should-a-user-be-notified-about-last-modified-time-of-bitcoin-conf-while-the-b

Conclusion: Attacker can do more than just making changes in config file and I realized such timestamp information may help in some cases although its best to solve it at system level for all important files by user with something like https://sourceforge.net/projects/iwatch on linux which is a tool for detecting changes in filesystem and send email notifications.