Add write_embodied to gridify

[trinker]

Add write_embodiedto gridify so that the csv is out put automatically with id (image numbers) and time. The following may be helpful for time:

fps <- 4
tot <- mp4_duration('foo.mp4')

part <- tot - floor(tot) 
vals <- seq(0, 1, by = 1/fps) 

difs <- vals - part
minval <- vals[difs >= 0][1]
maxtime <- ceiling(tot) + minval
sec_to_hms(seq(0, maxtime, by = 1/fps) )