Added Navigation widget project

Includes basic implementation of Navigation widget controller, model and
simple view.
Added Horizontal template
Adds Navigation templates

Added Vertical, Sitemap, Tabs templates. Changed the framework of the
Navigation project to 4.0
Extracted css in separate class
Added linkTarget
Added responsive transformations
merge from master
updated navigation model init
Added Navigation designer

Renamed all views for the navigation widget.
Changed bootstrap dropdown with select
Removed the toggle template
Fixed nav widget in template
Added tests for the navigation widget
Navigation widgets front-end changes
Update Dropdown.cshtml
Fixed validation problems in Horizontal navigation template
Merge branch 'NavigationWidget' of https://github.com/Sitefinity/feather-widgets into NavigationWidget
Added classes to the navigation widget designer
Merge branch 'master' of https://github.com:ElenaGaneva/Sitefinity/feather-widgets into NavigationWidget
Remove not used styles