update widget surveyor to track custom vs. flutter widgets

[pq]

Add a new column that tracks custom vs. flutter

So:

MaterialApp, 1
...

becomes:

MaterialApp, 1, flutter
...

[pq]

Fixed w/ afe2d140ca0de93acc8175f962fcaa29d6af73fb.

[pq]

FYI @jayoung-lee. Reports now look like:

MaterialApp, 1, flutter
HomePage, 2, *
PageOne, 1, *
PageTwo, 1, *
PageThree, 1, *
PageFour, 1, *
PageFive, 1, *
PageSeven, 1, *
SwipeButtonDemo, 1, *
FullPageRadioGroup, 2, *
TopPrograssBar, 6, *
FullPageHumanAnatomy, 1, *
FullPageAnalogTimePicker, 1, *
FullPageLocationAndImagePicker, 1, *
DataReviewAndUpload, 1, *

(where * is custom and flutter identifies flutter widgets.)