Add RACQueuedSignalGenerator
Add RACSignalGenerator operator for serialization
Unit tests for RACQueuedSignalGenerator
Replace generator initializers with class constructors

Purely an aesthetic choice, but class constructors look better than
+alloc/-init… when put into a chain of operations.
Replace generator initializers with class constructors

Purely an aesthetic choice, but class constructors look better than
+alloc/-init… when put into a chain of operations.

Conflicts:
	ReactiveCocoaFramework/ReactiveCocoa/RACQueuedSignalGenerator.h
	ReactiveCocoaFramework/ReactiveCocoa/RACQueuedSignalGenerator.m
	ReactiveCocoaFramework/ReactiveCocoa/RACSignalGenerator+Operations.m
	ReactiveCocoaFramework/ReactiveCocoaTests/RACQueuedSignalGeneratorSpec.m
:fire: RACAction :fire:

See #992.
Fix starting value for NSControl.rac_textSignal
Replace RACAction bindings with plain signals
Replace refresh control RACAction with signal generator
Refactor unit tests to match new bindings
Send the triggered control instead of `sender`

Sender arguments are very rarely useful, but being able to combine
event signals and figure out which control send a given event is super
handy.
Clarify that -rac_signalForControlEvents: sends the control
Merge branch 'queued-generator' into bye-bye-actions
Remove holdover subject in RACQueuedSignalGenerator
Add RACQueuedSignalGenerator.executing
Stub enqueuedSignals
Implement enqueuedSignals using a subject of subjects
Don't send completed before finishing error propagation

Without this `finished` flag, an error in the signal could result in
the subscriber of `enqueuedSignals` receiving a completion event,
because the subscriber’s disposable is disposed before the error is
actually forwarded.
Tests for enqueuedSignals
Update docs and deprecation messages