Cleans up pulsesrc changes.

Removes unnecessary try/catch in get_audioinput_bin.
Simplifies get_sources() method.
Adds TODO in get_sources.
Cleans up  audiopassthrough changes.

Removes unneeded call to set_plugin_option().
Simplifies get_input().
Removes unnecessary int/float conversions.
Cleans up rtmp_streaming changes.

Removes unused intermediate values.
Removes unneeded str/int conversions.
Simplifies widget_load_config.
Cleans up usbsrc changes.

Removes unneeded try/catch, import, and commented line.
Fixed widget load bug for usbsrc.
Simplifies pip.widget_load_config() method.