Step select code area (if possible)

[LefterisXris]

Currently the CodeTour plugin works with a file:line reference.
However this seems to be fragile and not easily maintainable as code will change sooner or later and Step's lines won't be aligned.

We could work with references (PSI elements). However the PSI elements may also change but the good news are that we can hear on PSI element changes and automatically update the Tour Step as well.

In addition, it would be nice, if user would be able to select a code block, instead of a single line, so that this block would be highlighted on Step Navigation.