Fixed bug where deleting a region could result in a crash

- Add pacemaker refractory periods and timing intervals to diagrams
- More options for positioning measurements on diagrams

Bug fixes

Changes in relative size of image and ladder are now persistent.

More options to stylize impulse activation and block symbols

Add labels to marks
Increase font size of measurements
Fix sandboxing issues
Bug fixes

Fixed memory leak bug that could crash the app
Other bug fixes
Fix typos in Help