change plovr to use git subtrees, and build on prepublish

Hello @nicks, 

Please review the following commits I made in branch 'nick-subtree'.

0b053497c8fb369f32670a5d750864a95948e791 (2014-08-18 12:53:16 -0400)
use the new fancy-pants method for building SoyFileSets

239d93bbb00c4fd310898f6980e16196a61c2bfe (2014-08-18 12:08:26 -0400)
change plovr to use git subtrees, and build on prepublish

28aaab311fd5aef840a45d71df73c223d8fc580b (2014-08-18 10:55:14 -0400)
remove closure compiler,lib,templates from the repo

R=@nicks