Support nested functions and classes

**Is your feature request related to a problem? Please describe.**
As said in REAMDE, the extension does not support nested functions/classes.
This would very much expand the extension's functionality and use cases.

**Describe the solution you'd like**
When moving a function inside an inner class, it should know to move inside that class (and not brake the file). Same in an inner funciton.
F.e. if I have a function in javascirpt with 2 inner functions in it, they should be able to switch positions, but not go outside of the outer function.

**Describe alternatives you've considered**
The only way to bypass this is to copy the inner function/class to another file, perform the changes, and then copy them back in (not so nice and sexy).
Right now, when dealing with inner functions/classes it is better to just cut and paste instead of use the extension.