contentcreator should ignore .DS_store and other dot files

[tisto]

contentcreator complains about ".DS_Store":

2021-12-06 10:32:35,522 - ERROR - Error in file structure: "/Users/timo/workspace/XXX/content_creator_beispiele/.DS_Store": 'utf-8' codec can't decode byte 0xaf in position 347: invalid start byte

we should just ignore dotfiles by default.