Improve search capabilities

[gsilvapt]

• Allow searching case sensitive keywords
• Allow searching full file contents instead of just title
• Allow searching in date ranges, since the main directories are a timestamp.
• Allow searching for tags, which will require implementing a tagging system for the notes (created its own issue for better tracking in Implement a tagging system for notes #42)

Each feature can (actually, it should) be a separate branch/PR.