Remove redundant :-moz-placeholder styles

No need for old Firefox versions support.
Use license object instead of licenses array
Update grunt paths
Merge pull request #12612 from ZDroid/grunt-path

Update grunt paths
use Less' extend feature in btn-group-lg etc.
Merge pull request #12605 from ZDroid/license-object

Use license object instead of licenses array
Update jzip to v2.1.0.
bs-raw-files-generator.js: use the global directive to define the `btoa` variable.
Merge pull request #12616 from twbs/jszip

Update jzip to v2.1.0.
Merge pull request #12613 from twbs/sized-btn-group-extend

use Less' extend feature in btn-group-lg etc.
use :extend in thumbnail Less
use :extend(.img-responsive) in Carousel's Less
Merge pull request #12621 from twbs/carousel-img-responsive-extend

use :extend(.img-responsive) in Carousel's Less
Merge branch 'master' into thumbnail-extend

Conflicts:
	dist/css/bootstrap.css
Merge pull request #12502 from ZDroid/moz

Remove redundant :-moz-placeholder styles
Merge pull request #12620 from twbs/thumbnail-extend

use :extend in thumbnail Less
property order because @zdroid <3
Integrate ZeroClipboard to easily copy code snippets