Add additional settings to show/hide elements when viewing .note files

[james-xli]

This PR proposes adding a few simple on/off settings for viewing .note files. I find these nice to have for a cleaner viewing experience, especially if I just want to look through many pages and am not planning to do much exporting.

All three of these settings look and work fine when used independently of each other in different combinations.

I haven't actually tested in combination with #24, but I expect these changes to work fine together.

Defaults/current behavior

The default settings shown below preserve the current behavior of the plugin:

My test note looks like this:

Hiding the table of contents and page number headings

Switching "Show table of contents" OFF removes the table of contents and the page number headings:

Hiding export buttons

Switching "Show export buttons" OFF hides the buttons:

Collapsing recognized text

Finally, switching "Collapse recognized text" ON tucks the recognized text under an HTML details element:

Clicking on that element expands it to show the text:

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Thanks for considering these unsolicited changes!