Implemented strikethrough using basic execCommand
Basic architecture for keyboard shortcut
Implementing keyboard shortcut
* Working
  - tab
  - shift + tab
  - ctrl + shift + delete
  - arrow up
* Known Issues
  - arrow down doesn't find following note if it's note in the current subtree
  - ctrl + shift + arrows if previous or following note is not in current collection
Implemented findFollowingNote recursively
Ticket0093 Wire up all other basic keyboard shortcut
* Ctrl + shift + arrow
  - Work only within a collection (same depth)
Implemented jumpNoteUp for any depth
Working on refactoring
Refactoring Note.Tree
Ticket0436: jumpPositionDown should always jump a note