Add support EXTTV tag

[Gemorroj]

Add support EXTTV tag (see request #4).

it defines language and groups TV programs are in (for instance Radio Salomon --> #EXTTV:Radio;slv; = its Radio and its language is Slovenian)

Need documentation for implementation.

[Gemorroj]

EXTTV format:
#EXTTV:tag[,tag,tag...];language;XMLTV id[;icon URL]
example:
#EXTTV:nacionalni,hd;slovenski;SLO1;http://cdn1.siol.tv/logo/93x78/slo2.png

[Gemorroj]

possible interface:

getTags(): string[]
getLanguage(): string
getXmlTvId(): string
getIconUrl(): string|null

[Gemorroj]

Implemented