EncodingProfile.setElementProperties

This allows setting the muxing/encoding element properties.

**Set properties generically**

[element-properties, boolean-prop=true, string-prop="hi"]

**Mapping properties with well known element factories**

element-properties-map, map = {
     [openh264enc, gop-size=32, ],
     [x264enc, key-int-max=32, tune=zerolatency],
 }