First try on network proxy configuration
Using the proxy on main window.
Proxy settings not being saved.
Added an icon
Merge branch 'network_proxy' of https://github.com/ammachado/zeal into ammachado-network_proxy

Conflicts:
	zeal/zealsettingsdialog.cpp
	zeal/zealsettingsdialog.h
Merge branch 'ammachado-network_proxy'
Added the icon to zeal.desktop