Optimization for search

[emdoe]

1. Display contents in the search result (and highlight the keyword)
2. Provide an option to auto-clear the previous search terms (I'm note pretty sure which one should as the default)
3. Highlight the search term in the note
4. Provide a search function in the note page and could let user quickly jump to the corresponding location
   1. search term occurring in user's note should be highlighted, too
   2. it would be great if the located terms not at the very top of the view (I think it will cost more time to let user notice their result is there. And maybe it would be better if it's around the center of the page?)