Add command line option(--set-profile=) to set active profile.

Fix #5 
Here I added simple profile-switching command line option.
If set, it'll override default or saved value for last profile.
Please take a look and give me any suggestions.
Is it OK? Or this option should be temporary and should work only for one run?

I've changed profile initialization a little.
It's some kind of nightmare inside Settings.cpp with all these static functions and members.
I think it should be refactored somehow.

Also it seems that my QtCreator used wrong tab size. I'll fix them and re-push the branch.
What settings do you use for tab size?