Add filtering and hint function to the icon cheatsheet

[Shanfan]

Hello Sergey,

Thanks for putting together the Iconic Font. It's very useful!

While I'm an active user of your icons, I would like to propose a UI update to your cheatsheet page, to make it easier to browse and filter. Main features I added:

• Type to filter icons by icon name or by keywords
• Added a keywords txt file to tag icons with metadata. i.e. search is tagged with magnifier, so when I type magn in the filter box, I can find the search button.
  • This keywords file is just start, hand typed by me. But if more people join to give keyword description to the icons, the search-filtering would be easier and easier.
• Added a hint area for the icon encoding. I know you have a modal popup on the Icons page. I adding encoding here to make it handy.
• As you scroll the page, the filter box and encoding hint will be sticky to the top of the page.
• I removed the header image because I think it's a little distracting, especially since the header is the same on every other page.

I made the content changes directly to the cheatsheet.html. The UI styling and behavior are handled by 2 new files cheatsheet.less and cheatsheet.js. So it should not interfere with other pages. If there's any Grunt production flow I missed, please pardon me, and I'm happy to make adjustment to my code to comply with your workflow.

I attached a few screenshot to demonstrate the features I proposed. Let me know what you think!

Thanks!

• Landing on the cheatsheet
  
• While the header scrolls out of the viewport, the filter-hint remains on top:
  
• Typing star will return all the icons named or tagged with star