Implement pen colour and erase.
Add lazy brush cursor (better than nothing).
Change style from FullScreenTheme to NoTitleBar because there is no need to show titlebar anymore.
Trial code for opening video after encoding. Commit for record purpose.
Cleanup merge encoding code to hope fixing that sometime video becomes later and later problem.
Fix crash problems. Add "Merge again" menu for workaround purpose.
When back pressed, query before finish. Remove obsolete menu handling code.