FIX: small typo caused error on wmsize
Small GUI tweaks
FIX: changed default wxh value for collage to 0. As the new
function causes to always return bigger sizes.

This makes important always set a both widht and height in modes:
Normal mode
Crop mode

Concatenation and Zero geomtry modes uses w and h in different ways
and it's not necessary to set both.
FIX: error if size 0 or empty in any collage mode

FIX: If collage only kra or ora files final output written in tmp
folder. Now it checks the correct path, the original.

FIX: GUI shortly not responsive after finishing converting, renaming or
rendering ora files.

Minor string update
FIX: If preset empty do not add to combobox
FIX: Do not get img src on every call. Now it only gets consulted
before rendering watermark images.
ADD experimental drag and drop support
FIX #44 : First draft of saving presets between runs.

To activate. In presets.config file change the value of
artscript(remember_state)

to 1, like this

artscript(remember_state)="1"
DELETED: binary windows tkdnd files. They are not necessary, the script
is not functional on windows yet