Collect and save note view stats

[DarthVanger]

Store note view stats in a file in the NeuralNotes/.neuralnotes-data/ folder. The idea of a dot-folder is inspired by .git/ folder. If you can come up with a better name than .neuralnotes-data/ would be great :) In that folder create a file to store the notes views stats.

It should store:

• note total views (+1 whenever user clicks on the note)
• note edits (+1 whenever user changes note name or content)
• last viewed date
• last modified date

This data is going to be used to define how the notes are displayed on the mind map, see https://github.com/DarthVanger/NeuralNotes/issues/69