Only display charts for active currencies

Fixes #605

Types of changes

[ ] Bug fix (non-breaking change which fixes an issue)
[x] New feature (non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to change)

[x] I have read CONTRIBUTING.md
[x] I fully understand Github Flow.
[x] My code adheres to the code style of this project.
[N/A?] I have updated the documentation in /docs if I have changed the config, arguments, logic in how the bot works, or anything that understandably needs a documentation change.
[N/A] I have updated the config file accordingly if my change requires a new configuration setting or changes an existing one.
[x] I have tested the bot with no issues for 24 continuous hours. If issues were experienced, they have been patched and tested again.