More radius/sigma by default

[WhyNotHugo]

I understand that how much blurring looks good in extremely subjective, however, with the current defaults blurred text is easily readable (partially defeating the idea of locking my screen).

I had to push radius and sigma up to 15 for text to become unreadable (but you can still tell it's text). Maybe I overdid it a bit, but I'd like to proposed to bump the defaults a bit so that i3lock -f makes text unreadable by out-of-the-box.

[karulont]

This is hard to get right for all users. Current defaults are dependent on the screen resolution. And as far as I have tested them, they make my terminals unreadable on all resolutions.

You can check the relevant function in here.

Maybe you can suggest some better magic constants for it.

[ghost]

@karulont What are the default values for radius and stigma? What is the min/max value?