:bulb: Add data attributes on directory and file views

It’ll allow for complex theming of the tree view items through CSS
attributes selectors and without relying on another package that’ll
have to poll for changes (see DanBrooker/file-icons package).
Adds specs testing data attributes on tree view items
:lipstick: Use atom project method to compute relative path
:lipstick: Remove obsolete requires
Merge pull request #130 from abe33/feature_data_attributes

Add data attributes on directory and file views