* Improve exception handling
* Add transparent themes
* Add null annotations
* Use java.time classes instead of Date and magic numbers
* Upgrade XChart to 3.1.0
* Fix buggy legend position logic:
Reinitialize counter to 0. So it does not work on legend position counter values of previously created charts.
Use a local variable for the position counter instead of a field. This prevents issues when creating multiple charts simultanuously.
For XChart release notes see:
https://knowm.org/open-source/xchart/xchart-change-log/
On newer XChart versions there is an issue when using customized grid lines:
https://github.com/knowm/XChart/issues/628Fixes#1183
Related to #2501
Supersedes #2415
Signed-off-by: Wouter Born <github@maindrain.net>
