git-gui: Rename fields in blame viewer to better descriptions
Calling the commit message pane $w_cmit is a tad confusing when
we also have the $w_cgrp column that shows the abbreviated SHA-1s.
So w_cmit -> w_cviewer, as it is the "commit viewer"; and
w_cgrp -> w_amov as it is the "annotated commit + move tracking"
column. Also changed line_data -> amov_data, as that list is
exactly the results shown in w_amov.
Why call the column "move tracking"? Because this column holds
data from "git blame -M -C". I'm considering adding an additional
column that holds the data from "git blame" without -M/-C, showing
who did the copy/move, and when they did it.
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>