Simplified and hid the logic of creating URLs in controllers

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I found a problem in some cases with the default budget. I fixed them by further simplifying the way URLs are built and hiding most of the nasty logic in private functions inside BaseController.

Also I gave UserController some love by inheriting BaseController :))

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@dauby88 I always promise it's the last one but let's hope this is the last one :)) it's related to the 'default' budget.