Sort images by filename in active-imageviewer. It's static sorting, that is, newer images will be appended to grid view end. Reopen imageviewer to sort them again. I think we can implement dynamic sorting using QSortFilterProxyModel as the base class of MetadataModel instead of AbstractMetadataModel. The sorting is case sensitive too. I have not figure out how to solve this yet.

CCBUG: 284672
(cherry picked from commit 3531ed4599c2fb9e2ff3440f078e09dc5f0c132d)