sync: add condition support

[kbkpbot]

Just like go.Cond.

[huly-for-github]

Connected to Huly®: V_0.6-22939

[enghitalo]

Why do you have an array of Channels?
If you are using Channels, why are you blocking the thread with a mutex?

[kbkpbot]

Why do you have an array of Channels? If you are using Channels, why are you blocking the thread with a mutex?

1. We can replace array of channels with array of semaphores. This is just for signal, broadcast working.
2. By using channels, we can use select with timeout.
3. Before enter wait, a user-defined mutex must be held.

[spytheman]

Excellent work.