Speed up linting and formatting by using more specific paths

[rniemeyer]

We found that we could get a considerable speed boost in linting and formatting by being more specific about the files being included. Including all js files and then excluding node_modules and other paths takes gulp.src considerably longer.

• removed sourcePaths as it did not seem to be used
• updated sources default to be more specific
• removed exclude, as the format and lint tasks no longer need that option

We are also using gulp-file-cache to only lint/format changed files, but I did not include that in this PR, as it writes a cache file that would need to be added to any projects .gitignore. This functionality can easily be added, if it is desired.

As an example, here is running gulp format on seriate:

Before:

[15:25:56] Starting 'jshint'...
[15:25:57] Finished 'jshint' after 1.02 s
[15:25:57] Starting 'format'...
[15:25:58] Finished 'format' after 908 ms

After:

[15:26:20] Starting 'jshint'...
[15:26:21] Finished 'jshint' after 456 ms
[15:26:21] Starting 'format'...
[15:26:21] Finished 'format' after 367 ms

[calvinb]

All good things are worth waiting for.

[digitalBush]