Fix timeline not loading older messages

[karaxuna]

Change-type: patch See: https://www.flowdock.com/app/rulemotion/user_happiness/threads/7NZvqy1kZMKauU_gaEgLG6zcuRI

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When fetching timeline events, limit is set to 20, but most of them may be events that are hidden by default, like: create, update, formula re-evaluation... So we end up seeing 3 messages which does not fill vertical space. There is a code in ui starts fetching more events if the scrollbar is on beginning of list, except if it's not already loading (which is the case when loading initial data), so nothing happens:

In this pr, we check scrollbar location after loading initial data and fetch more if it's on the beginning of the list.

[LucianBuzzo]

FAIL lib/Timeline/tests/index.spec.tsx (30.552 s)
  ● Events are toggled when the event in the url is one of type UPDATE

    TypeError: scrollAreaRef.current.scrollTo is not a function

      64 |              },
      65 |              scrollToBottom(options: any = {}) {
    > 66 |                  scrollAreaRef.current!.scrollTo({
         |                                         ^
      67 |                      top: scrollAreaRef.current!.scrollHeight,
      68 |                      ...options,
      69 |                  });

      at Object.scrollToBottom (lib/InfiniteList.tsx:66:29)
      at Timeline.componentDidMount (lib/Timeline/index.tsx:119:30)