Update jquery to v1.11.0.

Also use the one from Google's CDN.
fix duplicate id in HTML
drop iframe attributes for CSS styling

From https://github.com/twbs/bootstrap/commit/f4bb660974699f4336d22385e104347f6bd4dce0
add alt text to images
fill out previously empty img alt texts
import HTML5 validation task from Bootstrap; fixes #282
Merge pull request #291 from twbs/html-validation

add HTML5 validation Grunt task
_config.yml: Remove unused variables.
Improve package.json.

Use `license` property and remove `ratchet` keyword.
Remove `grunt banner`.
Run `grunt dist`.
Add banner to the minified JS.
Update cssmin options.
Enforce Unix line endings.

Backported from https://github.com/twbs/bootstrap/commit/f2dab82d307259c9029e21fc5020ada482b0df7c.
Merge pull request #319 from twbs/ZDroid-package-json-banner

Improve package.json and Gruntfile
Merge pull request #321 from twbs/line-endings

Enforce Unix line endings.
Fix a couple of CSS issues.

* remove duplicate property
* fix incompatible property for `background-color`
* remove unit from zero
Merge pull request #320 from twbs/css

Fix a couple of CSS issues.
Merge pull request #308 from twbs/jquery

Update jquery to v1.11.0.
Pulled from upstream-master, fixed merge conflicts.