Allow the links in the oa_user_badge to be modified

This is needed by the oa_workbench module to add the "My workbench" link to the user badge.

Also, this PR renames oa_dashboard_preprocess_* functions to template_preprocess_* for the theme callbacks the oa_dashboard defines. You can see these docs for the full info:

https://drupal.org/node/223430

But the short version is that a module should use template_preprocess_* when it's the one defining that theme callback. The moduleName_preprocess_* is for *other* modules. It's pretty much the same difference between hook_blah() and hook_blah_alter() - the former runs first to setup the initial data and then subsequent ones can alter it.

I hope that makes sense!