add templatedata api check

based on the bug report, i have added an api check for templatedata
that allows the extension to work without it.

i have also updated the INSTALL instructions to reflect the current
intent and limited MediaWiki tempalte use.

Bug: 59085
Change-Id: Ia9d10b6de48a54f803699d296f11b177ab2174b4
Merge "add templatedata api check"