Wait for ExecCommand before colorizing

[mheinzler]

ExecCommand uses a short timeout internally to append the data to the view. If this timeout isn't fired fast enough the regions can't be colored. A simple solution is to also add a timeout to the colorization.

This could still be improved a little by checking whether the regions are within the view size, and only use a timeout if they are not. That would remove some rare flickering introduced by the timeout.

[jfcherng]

Disclaimer: I am not using the on_data mode so I wont test and merge this PR.

I make this disclaimer just because it looks like I am the only active maintainer in the repo.