Enhanced FLASHCARDS FILTER and PREVIEW MOD

With Anki, we can filter specific cards into « virtual » deck and review them without having them rescheduled.

Also the following filtering parameters from the Anki application should be also available in RemNote

- is:learn for cards in learning (red ones)

- is:review for cards to review (green ones and green ones that have turned red)

- is:buried for cards buried until tomorrow

As well as the following filters:

- prop:due=1 for cards to review tomorrow

- prop:ease!=2.5 for cards whose ease is different from 2.5

I really think that the only thing RemNote is missing is a powerfull custom portal/deck filter system similar to Anki, allowing us to do everything mentioned above.