Adds option to use any html instead of index.html

Adds `phonegap.config.html` to change main page `"index.html"` to any `"other.html"`.
* Simply moves `"other.html"` on top of `"index.html"`.
* Optional : `phonegap.config.html` is ignored if omited.

Handy when same project shares different use-case (web, phonegap, etc...) and different index.html are to be used.