Output some error when require-dir tasks fails

It could be useful to see the results of the require tasks especially if there is an error.
Merge pull request #426 from alexanderchan/patch-1

Output some error when require-dir tasks fails
Fixes #441 - add custom logPrefix for BrowserSync
gulpfile - add `logPrefix` to the other browserSync instance

and single-quotes
Added some styles, working on tour nav headings and removing tour-nav
deleted dist
Merge branch 'master' of https://github.com/google/web-starter-kit