Note "Tagging"

[dullage]

Add the ability to "tag" a note by using a hashtag anywhere in the body (e.g. #work). Notes could be tagged multiple times.

This change would also require the ability to view a list of all tags used and the notes associated with each tag.

I should be able to use the search index for this but I would need it to index hashtags (currently it indexes "#work" as just "work").

Also consider including the tag itself in the search results i.e. if you search for "work" and there is a "#work" tag then display #work as the top result allowing the user to quickly navigate to notes associated with that tag.