Update documentation

Commit bad4a21 moved the Gruntfile from `src` to the root folder,
therefore `npm install` should be run there.
Merge pull request #1029 from jacquerie/tidying-doc

Update documentation
Removed some unused files
Merge pull request #1033 from wibblymat/unused

Removed some unused files
Correct page ID for use-existing-data.markdown
Merge pull request #1035 from crhym3/correct-page-id

Correct ID for use-existing-data.markdown page