Add Ginga-HTML5 support for the document loader

[rafael2k]

As per ABNT NBR 15606-10, Ginga-HTML5 is a new Ginga subsystem, and it should be supported by Ginga profile D SBTVD receivers (together with Ginga-NCL subsystem).

[Ronkiro]

bump, i think we'll need this ready for TV 3.0

[alanlivio]

I totally agree that should be supported. Just to remember what has been done in this:

• first version when having Directfb backend: use ncurses
• second version when having SDL backend: use Berkelium (chrome-based)
• last version uses Cairo-gst backend: uses Chromium embedded by PlayerHTML.cpp but is currently, not stable.

Other possible approaches are:

• use Webkit inside Cairo context
• use Webkit inside GST (nclua standalone proposed by gflima)