Fix outdated information on Animation page

I know this conflicts with !5 (merged), but:

• little things like "New Frame" => "Create duplicate frame" are easy but really important; even a smart person would assume that "New Frame" can be replaced by "Create Blank Frame" but blank frame would remove the content
• it says to use Shift + up arrow, but doesn't say which tool to use, so the shortcut wouldn't work (and the sentence was broken too)
• this page still contains information "Krita cannot render animation" and only later, at the end, there is a not "actually it can!", it's not really good tbh, what if someone reads "Krita cannot render animation to a video file" and stops reading because clearly Krita isn't what they want?
• and... well, I know this whole tutorial will need to be redone, possibly, with new screenshots when Emmet and Eoin will be at least partially done with animation. However it will happen in at least a few months, and I think it would be better if we had old screenshots but accurate text than a tutorial that cannot be followed by newcommers.

My changes:

• I removed half of the rendering info and just added a link to Render Animation page instead
• I removed some of the "Great, Krita 3.0 has animation now!!!" - I mostly just removed the mention of the version; if needed, I can add ..versionadded:: at the beginning of the page
• I added info that now all layers are pinned by default
• Some little proof-reading (added a period, changed "as" to "as well as")

Hope it's not too much of a trouble...