Shadowing of variables detection

[orchestr7]

Diktat should be able to detect shadowed variables as it can cause serious issues.

Name shadowing can cause following issues. There should be no shadowing.
infinite loop:

fun main() {
        var x = 0
        while (x < 10) {
            var x = 0
            x++
        }
}

[orchestr7]

#426 should help to create the logic next time