Make controllers before_filter free.

[iffyuva]

This helps in deriving from controllers, and specifying them {refer to exp-multitenant-support branch}, and adding filters the way user wants. At present, there is one before_filter can_administer?, and its too difficult to add any filter before it. One can do skip_before_filter can_administer? and redefine before_filter sequence, but user should be given more control w.r.t controllers.

[iffyuva]

@Aksh93 can you pick this up?

[akshaysasidrn]

@iffyuva Yeah, let me go through it.

[stale]

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