Add an advanced mode for calculator

Following your comment, I installed it. While I do like some features (like swipe in the keypad) I still think it is better to make the 'stock' app better than to install several to do the same as a good one. I expect at least the set of features of N900's calculator.

Speedcrunch however has the advantage of being free software, so moving away from the stock calculator means relying on one less piece of proprietary code. Of course, that doesn't matter to everyone.

The main interest of having stock app is the integration. If you really want to rely on less proprietary code, you will choose Mer over Sailfish. And it's not like the stock calculator and speedcrunch are the only calculators available. Nearly each desktop already has its own.

Make the default one good enough, and no other will need to be made. The default is too "basic", and even if you can install another one, I do not think it is a reason good not to make the default one better. I do not expect it to be done over night either and other things are more important.