UI: Enable video output format advanced option

This allows using NV12, I420, or RGB output video formats.  This option
will set what obs itself outputs frames as.

It's important to note that this is only ideal for specific FFmpeg
encoders that support the desired video format; for example, if you use
RGB and use the huffyuv encoder, huffyuv will now properly output in RGB
instead of YUV NV12/I420.

I420 is useful for eliminating the NV12->I420 conversion for the
AVerMedia encoders, as AVerMedia encoders only support I420 input.

A second even more important note about RGB is that if the encoder does
not support the format you are using, it will be converted on the CPU to
a format that the encoder supports as it's encoded; so for example
setting the obs output format to RGB and then using x264 will be futile
and end up using needless amounts of extra CPU than if you just had obs
set to NV12, which is the most common and ideal format for x264.

In the future, native output of other YUV formats might be implemented
(such as YUV 4:2:2).

obs/forms/OBSBasicSettings.ui

@@ -2438,9 +2438,6 @@
                    </property>
                    <item row="0" column="0">
                     <widget class="QLabel" name="label_30">
-                     <property name="enabled">
-                      <bool>false</bool>
-                     </property>
                      <property name="minimumSize">
                       <size>
                        <width>0</width>
@@ -2457,9 +2454,6 @@
                    </item>
                    <item row="0" column="1">
                     <widget class="QComboBox" name="colorFormat">
-                     <property name="enabled">
-                      <bool>false</bool>
-                     </property>
                      <item>
                       <property name="text">
                        <string notr="true">NV12</string>