www/joomla3: svn move joomla31 joomla3

• Match origin to PKGNAME to align with the Joomla upstream only supporting the most recent 3.x release at any one time.

www/Makefile, MOVED: Chase Joomla rename joomla31 -> joomla3 + spelling fix

Reference: https://docs.joomla.org/What_version_of_Joomla!_should_you_use

PR: 204016
Approved by: ports-secteam (feld)
MFH: 2015Q4