hob: Hob should display warnings generated during parsing

hob: Hob should display warnings generated during parsing

-now Hob catches the warnings generated during parsing, and after the parsing
is completed, if there are any warnings, it shows a bar that contains a message
with how many warnings has encountered, and a button "View warnings"
-when "View warnings" button is clicked, Hob shows a dialog with the warnings;
if there more than 1 warning, you can use "Previous" and "Next" button to see them

[YOCTO #3215]
Signed-off-by: Cristiana Voicu <cristiana.voicu@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>