use localStorage for snippets cache

[Ciki]

However, I'm not sure now this is the right approach as it does not handle situations when localStorage is full (5MB)

[Tomas2D]

Very useful! +1

[becygroup]

@Ciki I think you can you something like localStorage.removeItem(snippetsOrHash); in loadSnippets function

[zipper]

It might be useful to make methods loadSnippets and saveSnippets available from outside this extension, so you can use them in another custom extensions. Eg. $.nette.ext('history').loadSnippets(...) as is in your forked repository.