Add tags

[SwiftDust]

Feature: lets the user add tags to their notes with a new input prompt.

• Ability to search by tags
• Ability to add comma seperated tags to new and existing notes (e.g. by a new prompt below Content)
• Ability to color-code a note e.g by adding color:blue (probably using a constants file) or color:#fffff (HEX)
• Handle errors with colors (for example if someone adds color:non-existent nothing will happen)