A LOT OF MEMORY LEAK

[UladBohdan]

due to my knowledge of c++
refactor required.

[UladBohdan]

We still have "segmentation fault" issue on application close.
We've always had it, it's time to fix it.

p.s. I guess it's the same with #15

[UladBohdan]

upd
most issues were resolved in #54
seems that the issues which are left are in removing Thumbnails.