[messaging] Replacing MessageFolder with picojson part 2.

[messaging] Replacing MessageFolder with picojson part 2.

+ FilterUtils::isMatching() overload for picojson::value.
+ Removed some getters/setters from MeessageFolder.
+ Removed unused FoldersChangeCallback::getFilter() method.
+ Simplified implementation of MessageFolder::isMatchingAttribute().
+ Removed stringToMessageFolderType() unused function.

[Verification] tct-messaging-*-tizen-tests 100% pass.

Signed-off-by: Michal Michalski <m.michalski2@partner.samsung.com>
Change-Id: I578dcbd7b9d4fb5650f0eca1ecb264a78aff8962