Add new instrumentations : changes in tabMorph & scrolling

[Julesboul]

This pull request allows to record scrolling by moving the scroll bar or by using mouse wheel.
Also it allows to record changes in tabMorph (= when you have tabs in a window and you're moving between them).

For now, there is some minor issues:

• recording tab changes produce a lot of record when it comes to the browser (Calypso), but we didn't find another way to get tabs' data.
• scrolling records may be important, but it seems to not pollute too much the list of records. If needed, it will be possible to merge/squash them into one or two events (building the history).