Dnn 4651 - html5 compatible

Modfications :
1) New site settings (printscreen in attachment)
New section in Site settings, advanced settings with name "Page Output Settings".
In this section 3 new settings :
a) PageHeadText : replace the static meta tags of default.aspx
On upgrades : no difference (like before 7.4)
On new installs : "not html 5 compatible" tags are removed
b) InjectModuleHyperLink (default true)
Gives the possibility to not generates the <a name="[moduleid]"></a> before each module in the generated html
c) AddCompatibleHttpHeader (default IE=edge)
Add the X-UA-Compatible to the http headers
This replace the meta tag that was included in previous version in default.aspx
2) Not html 5 compatible copyright meta tag is removed
People we want to use this in the future have to add them manually in the new PageHeadText setting
3) DDR Menu templates of the gravity skin are updated to not generate hyper links with a empty target attribute
4) correction to the default skin

Remark : the default page shown is not yes html5 compatible.
A empty page is html 5 compatible
Used validator : https://html5.validator.nu