Handle transcluding templates outside of the template namespace properly

Stop prefixing all requested titles with 'Template:', and don't try to use
colon prefixes when transcluding except when deliberately transcluding from the
main namespace.
(A title prefixed with a colon on MediaWiki is used to create a link to
something that would normally be included as a File/Category)

Bug: 52609
Change-Id: Ia67f9054a56e71153339f961bbbcadb565115748
Merge "Handle transcluding templates outside of the template namespace properly"