Enhance locks of handlers
- [x] Freehand, Highlighter `defaultLock=true`

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- Editor has `activeHandlerLock`
- Handler has `defaultLock` in options (not `lock`)
- If a handler is `defaultLock=true`, set `activeHandlerLock=true` when it activates
- When a handler action complete, if `activeHandlerLock===false` activate default handler (do in Handler, or do in Editor?)
- Set `activeHandlerLock=false` when call `activateDefaultHandler()`