handle GUI while checking file hash. Show show re-request dialog when hash is incorrect. TODO: re-request file to sender.

fix bug: assign jingle session id as sid in file_props, so that file transfer window gets updated correctly for the sender.

code added to trigger jingle ft session when needed

add jingle FT to gajim.gajim_optional_features

Also use sed to remove now unneeded Vim lines, 2to3 -f ws_comma to fix
some whitespace, and fix some other madness manually.

also use 2to3 -f ws_comma to fix some whitespace

holy diff batman!

One of the methods was duplicated. Additionally, apply a very few coding standards.