Sometimes we have folder around in the project that don't need to be
shown in the project tree. For git projects, you can just gitignore them
but for non-git folder based projects there is no way to do this.

With this commit, you can now specify a "exclude_folder_patterns" in the
.kateproject file like:

{
   "exclude_patterns": ["node_modules", "blah"]
}

and any file/folder that matches this pattern is ignored