Rewrite of the javascript part

[dedlfix]

Could you please have a look at dedlfix@1dbaa5a (comments added: dedlfix@4389b4d)

I tried to simplify the code, getting rid of some similar looking code in favor of functions. I also removed the two global arrays. Now a new editor is created when the filter changes to Ace, and removed when changed to other. Did these arrays have any purpose that is now gone?

Other changes:

• translatable labels (but no new language strings)
• made cookie names unique for each layout, snippet, and page part
• "last updated" message stays below the editor
• #add-part-button click event handler removed - doesn't seem necessary

Is there any other feature that I accidentally removed?

[marekmurawski]

This is huge, really! You've done really good work. I didn't check everything yet but it all seems to work flawlessly.

I really appreciate your work on cleaning this code. I couldn't find time and energy to untangle that mess 😄

I'll merge javascript rewrite alone, without the dynamic DB settings loading because of #4 reasons (stable-wolf-compliance).