Make new tags colorful

[NiloCK]

Current behaviour:

• only tags that existed at startup are given colors

Desired behaviour:

• new tags that are created at runtime should be given colors.

Difficulty:

Current color schemes are algorithmically determined, and are based on evenly spacing the n existing tags across a certain gradient. Adding a new tag bumps n to n+1, so the new color would have to either:

• sit 'unnaturally' close to two existing ones
• trigger a regeneration of all tag colors
• ?