[Dextrose] Backport bugfixes from sugar-toolkit 0.90/master

[Aleksey Lim]

0.90/master bugfix patches that might be useful to dx-2:

[PATCH sugar-toolkit 1/4] Not able to access files on external device from within an activity on new system d.l.o #10218
[PATCH sugar-toolkit 2/4] Do not break if the string contains no conversion specifier #2354
[PATCH sugar-toolkit 3/4] bundlebuilder: install mimetypes.xml and associated icon #2262
[PATCH sugar-toolkit 4/4] XoColor: don't choke if passed the wrong type (SL#1408)