diff: move diff stat addition to a common function

Signed-off-by: Kumar Appaiah <a.kumar@alumni.iitm.ac.in>
diff: move diff stat drawing to a common function

Signed-off-by: Kumar Appaiah <a.kumar@alumni.iitm.ac.in>
log: colour the diff stat

This commit adds custom log_read and log_draw functions that utilize
the diff stat drawing functions from the diff module. The absence of
the triple hyphen separator prevents direct usage of the diff drawing
functions.

Signed-Off-By: Kumar Appaiah <a.kumar@alumni.iitm.ac.in>
Switch log, diff and stage views to use column-based draw backend