Support a tag like h:1 for hiding items from the list

[Strubbl]

It would be nice to have this web app support hidden tasks. This is already supported by the Simpletasks Android application and well explained in their documentation:

Hidden tasks with h:1, this allows dummy tasks with predefined lists and tags so that lists and tags will be available even if the last task with the tag/list is removed from todo.txt. These tasks will not be shown by default. You can temporarily display them from the Settings.

https://github.com/mpcjanssen/simpletask-android/blob/master/app/src/main/assets/index.en.md#extensions

It would be nice if the webtodotxt application would support the same hidden tag as Simpletasks and automatically hide hidden tasks. Furthermore the filter menu should have the possibility to switch between showing hidden tasks and not showing them. Default option shall be to hide tasks with that special tag.

[EpocDotFr]

Sure, it's a good feature request. I'll look into it when I have time.

Linked to #4