statically unreachable code should be grayed out (or other visual clue)

[timotheecour]

I think visualD does this to some extent.
Examples:

version(none){
...
}
other examples:
static if(false){}
version(myversion){} //when not given in command line version identifier
version(OSX){} // when on linux

More complex case (could be supported later):
static if(some_CT_condition){} // upon rebuild, evaluate those
static if(isDynamicArray!T) {} //gray out if no code path leads to true

[aBothe]

For now, only version and debug conditions will be checked due to performance reasons.