[property view] implement a new input for custom icons

[zeroooing]

user can set a costom icon name, with suggestions
from a dropdown list greped by user's input

[zeroooing]

change event will refresh property view so that click event of datalist is not triggered..

[zhizhangchen]

Please put the above comment in the CODE, such like:
FIXME: The "change" event will refresh property view so "click" event of datalist is not triggered. We have to look up the ":hover" class here to decide which item is clicked

[zeroooing]

Fixed as john's comments

[zhizhangchen]

Please add a whitespace between "//" and FIXME :)

[grgustaf]

There were some tight loops making DOM changes; it's more efficient to batch them up into a single DOM change whenever possible. I added a follow-on patch to do that, please take a look and make sure it looks right.

Also, with the old code the list of icon names appeared above the control, floating above the outline view. I believe it would go below if there was room, but it notices there isn't and goes above. It would be great if you could do that here too, because it's hard to use your control when it's partially scrolled off the screen.

But nice job...

Please close this PR, I'm leaving it open to try to make sure you get my comments.