feat #548 add npmignore

Close #548. Close #576.
fix #577 Problem with vertical scrollbar inside selectbox widget when popupWidth = -1

When the popupWidth is equals to -1 the vertical scrollbar hides part of the selectbox popup content due to a problem with the overflow-y sets to Auto. With overflow-y equals to scroll it works fine.
refactor whitespace formatting
feat #445 leading tabs detection in the code

A grunt task is added to prevent checking in unformatted files
in the future. It's very simple now, just checks for leading
whitespace being a tab instead of a space.

Close #445.