Code hygiene: fixed issues reported by Sonarqube
Improved error reporting when downloading quotes from Yahoo
Set user-agent when downloading HTML tables

- sites return an alternative/mobile version if no user-agent is set
- log HTML if now quotes are found to support troubleshooting
- support more column labels: English labels

Issue: #114
Add json-simple library to product update repository
Update about dialog to include contributors
Replaced special import parsers with the new generic HTML table import
Release 0.10.0