Build: Specific copy:* and task descriptions

- Task descriptions are shown running `grunt --help`
- Adds new "assets" task for other files copied to the dist
- Move test/jshint call to the high level dist/debug chains
SCSS: Extract variables to common sheet

Fixes gh-3150
SCSS: Cleanup base imports
Bower: Don't exclude dot files

Some of these are required for the theme re-builds
Merge pull request #3173 from nschonni/v4-build-cleanup

Build: Specific copy:* and task descriptions
Lightbox: Added Close, Next and Previous i18n labels with keyboard commands and added some placeholder CSS
Merge pull request #3179 from pjackson28/lightboxwork

Lightbox: Added Close, Next and Previous i18n labels with keyboard commands and added some placeholder CSS
Merge pull request #3172 from nschonni/v4-variable-scss

V4 SCSS cleanup
Lightbox: Corrected i18n mis-reference
Merge pull request #3182 from pjackson28/i18nlabelupdate

Lightbox: Corrected i18n mis-reference
Test: add fake timer support to IE
Test: unit tests for session timeout plugin