Changed policy decision mechanism to use content resource throttle API

Changed policy decision mechanism to use content resource throttle API

Handling decision in NetworkDelegateEfl::OnHeadersReceived caused
a lot of troubles due to insufficient amount of information needed
to distinguish between page resources and downloadable files.
This patch replaces the original mechanism used with resource throttles.
It allows us to make better decisions regarding how to handle the
content we're dealing with.
Removed unnecessary code duplicating existing engine functionalities.

This patch contains following patches:
http://suprem.sec.samsung.net/gerrit/#/c/6663/ by Kamil Klimek
http://165.213.202.130:8080/#/c/68742/ by Michal Stefanczyk
http://165.213.202.130:8080/#/c/69608/ by Marcin Łapiński
http://165.213.202.130:8080/#/c/70054/ by Kamil Klimek
http://165.213.202.130:8080/#/c/71925/ by Maciej Skrzypkowski

Bug: http://107.108.218.239/bugzilla/show_bug.cgi?id=9488
Reviewed by: Kamil Klimek, Piotr Tworek, SeungSeop Park

Change-Id: I76a2799586c4902327add2e6827a05ae2b4ddd3c
Signed-off-by: Tomasz Czekala <t.czekala@partner.samsung.com>