DNN-4651

Make DNN W3C Compatible

Modfications
1) New site settings
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
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 true)
Add the X-UA-Compatible IE=edge to the http headers
This replace the meta tag that was included in previous version

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
- change AddCompatibleHttpHeader from boolean to string
- correction for initialization on install and upgrade
correction of the url of the dnn hyperlink in the footer to be html5 compatible
Merge branch 'development' of https://github.com/dnnsoftware/Dnn.Platform into development