Made Special:Contributions includable

This commit make Special:Contributions transcludable by changing
extended class SpecialPage to IncludableSpecialPage also it adds if
condition in execute function to avoid the inclusion of form when
Special:Contributions is transcluded into other appropriate MediaWiki pages.

Bug: 4365
Change-Id: I25c5cc3775b91fdc17c1209953d425c640e5bc77
Merge "Made Special:Contributions includable"