Fixing #55 : When we edite slides, the slide category is setted the first one in the liste and not the default one

...liste and not the default one
I don't think that `option:contains` is the most suitable function for matching this will cause errors, find will always select the last matched sub-string eg :
let's assume that we have this list of categories : `aa`, `ab`, `aaa`,  `aaaa` and `aabb`.
If the category is `aa` so the selected will be `aaaa`.
If the category is `ab` the selected option will be `aabb`.