Issue title: Refine plugin architecture
 Issue body: - Make Webapp and Crawler objects singletons
  - Remove instantiation out of init.php and in beginning of tests
  - Add instantiation to controller file
- Convert webappPlugin->renderConfiguration method to new controller architecture

 Comments: 
 Comment 0: First step:
http://github.com/ginatrapani/thinktank/commit/5725535118d465c22b0dc0e1a5b96c66b8953cbe

Next step: convert account page to new controller architecture, and suss out how the plugin will deal with that.

 Comment 1: Done:
http://github.com/ginatrapani/thinktank/commit/93bad80a3e34302ced2ca34b1a39ab77043f3329

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