Bug 913586 (Part 1) - Revamp Maybe<T> to be usable in many more situations. r=waldo

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extra : rebase_source : 33326a59f0458dbda493b1f90b88481507b7a46b
Bug 913586 (Part 2) - Update Maybe users in accessible. r=asurkov

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extra : rebase_source : 521f090c8b37137877011ee057573f7baa62c5cb
Bug 913586 (Part 3) - Update Maybe users in content. r=bent

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extra : rebase_source : 79526555fcb097068b9d0b54b90e35b0d53eb43e
Bug 913586 (Part 4) - Update Maybe users in dom. r=bz

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extra : rebase_source : 7b6159b00b3bf4f919b30f1bccc8939cc04fe526
Bug 913586 (Part 5) - Update Maybe users in image. r=tn

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extra : rebase_source : 694928307fd724af821f51374bcf6fefb28fef5f
Bug 913586 (Part 6) - Update Maybe users in js. r=luke

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extra : rebase_source : c5d23a7874de49e61b43f79b8eda744db0523c6e
Bug 913586 (Part 7) - Update Maybe users in layout. r=dbaron

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extra : rebase_source : 1bf45d1356d36269ca951b58ebf1e448313c55c5
Bug 913586 (Part 8) - Update Maybe users in netwerk. r=mcmanus

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extra : rebase_source : 9e5d4813ab463860a6339740e955a958b1902f8f