mergetool--lib: fix startup options for gvimdiff tool

Options are taken from <Git source>/mergetools/vim

Signed-off-by: Alexey Shumkin <Alex.Crezoff@gmail.com>
mergetool--lib: Add diffuse as a tool

Signed-off-by: Alexey Shumkin <Alex.Crezoff@gmail.com>
mergetool--lib: Add TortoiseMerge as a tool

Also added Russian translation of the added error message
"%s cannot be used without a base"

Signed-off-by: Alexey Shumkin <Alex.Crezoff@gmail.com>