Fix delay behavior in Controller

[lxl66566]

Depends-On: #3

In previous Controller design, every generators will take one DelayStrategy, it will delays on each next() call.
If i convert a GeneratorGroup into Generator, the new Generator will take the DelayStrategy of the first generator in the group. If there's different DelayStrategy in the group, it will be lost.

The solution is to make DelayStrategy as an Iterator that contains a sequence of each DelayStrategys, in the same amount of generator op sequence. So when converting GeneratorGroup into Generator, the DelayStrategys will be chained and will not lost.

This change is based on that an op sequence in the generator must be finite.