[lmi] Size of combobox buttons under Linux

[Vadim Zeitlin]

 Hello,

 I've looked closer into the problem with the combobox buttons being too
fat under Linux and unfortunately all I can say is that it seems that this
(30px) is their default width. In principle it can be changed by
manipulating GTK+ arrow-scaling property, however at least with theme I
tested with, I couldn't make it work. You can see if it works for you by
creating the file ~/.config/gtk-3.0/gtk.css with the following contents:

---------------------------------- >8 --------------------------------------
* {
  -GtkComboBox-arrow-scaling: 0.5;
}
---------------------------------- >8 --------------------------------------

Setting scaling to 2 works for me and makes the arrow even fatter, but
setting it to anything less than 1 doesn't seem to have any effect, I don't
know why.

 Also, even if we could change it, in theory the default value should be
used and it's actually the (subjectively nicer looking) wxDatePickerCtrl
arrow that is wrong and should be made of the same width as this one.

 I think the best, both aesthetically and functionally speaking, would be
to replace wxComboBox here with wxChoice. While under MSW a read-only
wxComboBox and wxChoice are one and the same thing, elsewhere this is not
the case by just changing the former to the latter (and removing wxCB_XXX
styles not necessary with nor supported by wxChoice) in skin.xrc, you can
see that it looks much nicer.

 Regards,
VZ