Pension calculator content amends

https://www.pivotaltracker.com/story/show/59817116
Nearing retirement - thresholds changed

https://www.pivotaltracker.com/story/show/59817116
"Currently functions when someone is within 4 months and 1 day from
state pension age but it should be within 4 months and up to 1 day
before state pension age."

* Whitespace fixes
Remove pension estimate if < 35 days away

https://www.pivotaltracker.com/story/show/59817116
Merge pull request #604 from alphagov/state-pension-calc-changes

State pension calc changes