Add automatic file tag suggestions by file content using Machine Learning

[SeanPedersen]

When a new file is added, automatically infer tags from semantically similar existing files tags.

Depends on #24

[SeanPedersen]

This feature is non trivial and hard to get right. False positives (wrongly added tags) will be really annoying.

Some possible mitigation's:

• be really conservative, e.g. only suggest few top matches (with high confidence)
• Analyze cluster variance for each tag and prefer low variance (high density / coherence)
  • This will prevent generic tags like eBooks being suggested for e.g. a scientific paper. Instead specific tags will be preferred, increasing signal.