use glob instead of fs.readdirSync since /less now has subdirs
rename generateCustomCSS to generateCustomLess for accuracy
enhance customizer to handle transitive Less @import-s
grunt update-shrinkwrap build-customizer dist
Merge pull request #13047 from twbs/fix-customizer

Fix customizer (see #13043)
Tweak JS style and the relevant JSHint and JSCS checks.
Comply to the new style.
Remove `laxbreak`.
Remove `boss`.
Enable `requireCurlyBraces`.
Enable `es3`.
Switch to using plain `if/else` statements when there's no assignment.

The minizer outputs the same code anyway, and this has better readability.
Minor whitespace changes.
Switch to `(function){..})()`.
More updates to the JSHint options.
Run `grunt`.