As I'm starting to learn to create a new altcoin, I found there is a remarkable difference between old and new Bitcoin/Litecoin Core wallet is that old versions (0.6.9 of Litecoin) have mining functionality integrated in the wallet with a tab and a button for it while new versions (from 0.7.0.1 of Bitcoin) don't.

So my question is from which version the mining functionality removed from wallet? Is there any change logs/release notes/statements that say about this change? And can someone tell me why we should separate it from the wallet?

I really want to see if I can re-integrate this functionality back to the wallet as most of my clients are low-tech and a button "Mining" will be definitely much visually easier then running bunch of lines of command in the terminal.

I guess some of you may then start to tell me to stop creating new altcoins but my clients really want to have a new bitcoin-like currency for their private business so I think you will unlikely to see it public elsewhere if you're not part of the business so never mind. :)

Any reference links or articles or kinds of help will be highly appreciated. Thank you!