Add ability to pin notes

[michaelkennethdavid]

This pull request adds the ability to pin notes within the application. Notes can now be pinned by adding #pinned anywhere in the note content.

• Added functionality to mark notes as pinned using #pinned.
• Optionally display pinned notes on the home page by setting FLATNOTES_HIDE_PINNED_NOTES to false. Pinned notes are hidden by default on the home page.
• View all your pinned notes via the menu button: Menu -> Pinned Notes

Default home page / FLATNOTES_HIDE_PINNED_NOTES: "true"

[dullage]

Thanks for the PR @michaelkennethdavid.

There's a lot to like here and in general, I like the proposed change. It does, however, commit flatnotes down a particular route when it comes to things like pinning and so I need to mull it over first. There's also a couple of bits I'm not entirely comfortable with, namely:

• The increased "busyness" of the home page.
• The duel calls to the API on load.

I'll come back to you on this.

[michaelkennethdavid]

I understand. Let me know if I need to change anything.