Added non-existed open graph and twitter properties

[ugurhangul]

Added non-existed open graph and twitter properties along with new open graph and twitter groups,
Added default option for dropdown property,
Added SeoVideoEditEditor media picker property,
Solved MetaFieldsTagHelper.cs null exception bug when MediaPicker property null,
Facebook App Id title changed.

[ugurhangul]

Known bug;

Image and Video editor fallback values sets as class name

[dederuhi]

great enhancement

[patrickdemooij9]

Hi @ugurhangul

Thank you for this huge Pull request! It looks very good! I did also spot the same issue as you with the Image and Video editor fallback values sets as class name. And now that we have sections for all the different social websites, the previewers probably should just use the corresponding one (so twitter section = twitter previewer) instead of all.

But other than that, this looks great!