Show dive import text updates in the progress bar

Show dive import text updates in the progress bar

Instead of using printf() to print the string updates ("Parsing sample
data" etc), introduce a function to show those strings in the graphical
progress bar itself.

Subsurface hasn't been a text-mode application in a long time ;)

This partially fixes the second todo entry from commit b0ba22a06879
("Show dive import error messages in the import dialog") and generally
makes for a more helpful import - at least for the largely error-free
cases.

Sadly, the messages that really come from within libdivecomputer itself
(like "suunto_vyper2.c:193: Failed to receive the answer.") when things
go really wrong are not caught.  libdivecomputer does have a notion of a
logfile (set with "message_set_logfile()"), but that ends up being
really inconvenient.

Maybe we could use some pipe setup or something. Oh well.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>