Add support convert icon to ICO format

This needed for Riot:

• Exec path:

# on DEB
/opt/Riot/riot-web
# on ARCH
/usr/bin/riot-desktop

• Initially program load PNG:

# on DEB
/opt/Riot/resources/app/img/riot.png
# on ARCH
/usr/lib/riot/electron_app/img/riot.png

• After program load ICO:

# on DEB
/opt/Riot/resources/webapp/vector-icons/favicon.ico
# on ARCH
/usr/share/webapps/riot/vector-icons/favicon.ico

Example config (ICO format not converting):

{
    "name": "Riot Web",
    "app_path": [
        "/opt/Riot/riot-web",
        "/usr/bin/riot-desktop"
    ],
    "icons_path": [
        "/opt/Riot/resources/app/img/",
        "/opt/Riot/resources/webapp/vector-icons/",
        "/usr/lib/riot/electron_app/img/",
        "/usr/share/webapps/riot/vector-icons/"
    ],
    "icons": {
        "tray": {
            "original": "riot.png",
            "theme": "riot-tray"
        },
        "tray-ico": {
            "original": "favicon.ico",
            "theme": "riot-tray"
        }
    }
}