MVP #tags for notes (blessed set of tags)

[bfollington]

First pass at implementing #tags into the app:

1. Create a set of blessed tags
2. Map those to colors
3. Derive note color from tags
4. Make tags clickable and indexable in DB

[gordonbrander]

One idea for creating a soft mapping between tags and colors:

• Note color can be chosen by user
  • Stored in header theme-color
• When choosing a color for a note, we look for the presence of certain "blessed" hashtags and/or slashlinks, which are associated with a color. These cause a color to be chosen by default.
  • However, user may later override.
• Blessed tags might get a special treatment

This creates the desired effect of recognition over recall, where a user recognizes "journal", "idea", etc, yet still gives users the ability to directly customize the color. The looser connection between color and "type" also could allow us to choose color based on things like embeddings in future.