Bump User Guide up to v5

This MR is in preparation for the CiviCRM version increment to 5

• This makes "5" display to the reader where previously "4.7" displayed.
• Any URLs pointing directly to 4.7 will be redirected to 5.

We should merge this after the switch to v5 is publicly announced and releases are available for download.

mentioned in issue dev/release#1 (closed)

mentioned in commit 11d138c9

merged