Enhance big dataset usability - step 1

Related to #395 (closed)

Help to make Baserow more usable with big data set:

• Remove hidden elements from DOM when they are not visible in Context component (better table loading/rendering time)
• Remove the throttle part of grid.js/fetchByScrollTopDelayed to avoid browser freeze by struggling when processing is longer than throttle delay (better scrolling experience)
• Prevent cell render that are outsive of the screen
• Prevent search update on table loading while search term is empty (better table loading time)
• Limit vertical size of the hide field component

with those enhancements I'm able to use a data set of 200columnsx400rows without too much pain:

• First table display drop from 10~15s to 2.5s
• Scroll is... working

Now the compromise:

• As the throttle is removed from fetchByScroll, for small dataset we can experiment a little difference while scrolling for long distance
• The vertical scroll is less fluid than before as we are rendering cells on the fly
• Some Context nesting are to be managed differently as closed context is removed from DOM (See changes)

• changelog.md has been updated if required
• Documentation has been updated
• Quality Standards are met
• The UI/UX has been updated following UI Style Guide
• New/Changed Premium features are separated correctly in the premium folder