V1.0 beta10

• Improvement: optimize "Go To File" and "Find in Files" by asynchronously searching.
• Improvement: add preference for max size of undo/redo history of code editor.
• Improvement: loading recent files lazily after clicked tab at the first time.
• Fix: no topics focused after deleting one or more topics;
• Fix: empty topic with children will be deleted when hits ESC during editing.
• Performance optimizing and refactor.