files-view: Ignore hidden directories in the templates folder

The hidden files can now be used as templates since commit 967b9d7c.

This change also caused that also hidden directories and their content is offered in the "New Document" right click menu. This change was not intentional and causes issues when for example git is used to manage the templates as the while .git file tree is offered there.

The similar issue can happen also with some hidden files like .gitignore, but there is not much we can do with it.

Let's ignore the hidden directories as a compromise.

Fixes: #1413 (closed)