Add "Age" column to tx view

[lrettig]

When looking at a list of transactions today you see layer numbers but no date/time information, which makes it hard to tell when a tx occurred:

Contrast this to the etherscan view, which shows an Age column:

Let's add something like this to all tx views.

[lrettig]

On etherscan when you mouse over the relative Age, you get an actual timestamp. Let's do the same.