Fix Version Check for IE11

IE 11 does not have MSIE string in user agent, so check for IE 8 causes it to break pages showing on IE 11. Check makes sure MSIE before comparing against IE 8
Carousel: Update IE browser check

Updates the IE browser check to utilize WordPress core functions instead of
attempting to test the browser agent string, which has changed format in
IE 11. This commit closes #172 and creates a new PR for the functionality
Carousel: Final tested fix for IE 11
Social Links: do not use anonymous function

Jetpack has to remain compatible with PHP 5.2
Clicking 'configure' no longer opens modal.

Removed a click listener for the configure link to open a modal with the
configure tab open, since the tabbed view is not used.
Close modal when ESC key pressed

Both landing page and settings page modals can be closed via the ESC key.
Merge pull request #445 from Automattic/ie_versions

  Carousel: fix Version Check for IE11 take 2
Merge pull request #810 from Automattic/add/esc-key-handler

Close modal when ESC key pressed
REST API: Return different errors.

Return different errors identifiers and messages in order to identify
the nature of the errors.
Remove module title from module description.

Add the title to the modal template instead.
Updated modal styles
Don't escape special chars in module titles.
Removed responsive featured h3 style
Adjust stacking context. Help menu is now under modals.