edit site via Piwik API

use "PKHelper::CPREFIX" to only write prefix once
add function to edit site via Piwik API
refs #2

link to piwik + auto login if username and passwrd isset (PS1.6)
Prestashop 1.4 fixes

fix class PKHelper (translations)
remove site manager from prestashop 1.4 (works but return error
successfull Update)
update help link to github wiki
refs #2

add piwik link to prestashop 1.4
add help link to github wiki
missing password field
remove php warning
remove php warnings
closes #2

add Piwik link (Prestashop 1.5)
add help link (Prestashop 1.5)