Replace old gconf with gsettings schema

mini-commander was removed and mixer applet moved to mate-media so I removed them.

Make check now fails with the following but I don't know why. if you know do let me know and I'll add it to this PR.
<pre>$ LANG="en_US.UTF-8" make check
Making check in po
make[1]: Entering directory `/home/sander/repos/mate-applets/po'
INTLTOOL_EXTRACT="/usr/bin/intltool-extract" XGETTEXT="/usr/bin/xgettext" srcdir=. /usr/bin/intltool-update --gettext-package mate-applets --pot

junk after document element at line 2, column 0, byte 45 at /usr/lib64/perl5/vendor_perl/5.16.3/x86_64-linux/XML/Parser.pm line 187.
/usr/bin/xgettext: error while opening "../invest-applet/data/Invest_Applet.xml.h" for reading: No such file or directory
ERROR: xgettext failed to generate PO template file. Please consult
       error message above if there is any.
make[1]: *** [mate-applets.pot] Error 1
make[1]: Leaving directory `/home/sander/repos/mate-applets/po'
make: *** [check-recursive] Error 1</pre>