Update iOS video capture and simple renderer

[nanang]

iOS video capture and simple renderer were actually already implemented, however it has not been maintained nor tested for long time due to lack of video support on iOS. This ticket will check and update the implementations.

Some additional features planned on the capture device implementation:

• native preview
• enumerate all available capture devices, e.g: front and back camera
• fast switch between capture devices

The simple renderer is a CGImage+UIView based renderer.

[nanang]

In 4824:

Re #1762:

• enumerate all capture devices
• fast switch between capture devices
• enhance simple renderer (a bit simpler, add capabilities)

[ming]

In 4834:

Re #1762: Add capability enumerations and native preview capability

[nanang]

In 4836:

Re #1762: Add I420/IYUV output format to capture devices.

[nanang]

In 4837:

Re #1762: Fix native preview not shown issue by starting capture session from main thread.

[nanang]

In 4838:

Re #1762: Support more capture sizes (was only 352x288) and automatically find the closest supported size from the requested size.

[nanang]

In 4853:

Re #1762: Fixed native preview cannot be stopped.

[ming]

In 4891:

Re #1762: Related to r4838, check whether the device supports the capture size before deciding to use it

[riza]

In 4902:

Re #1762: Change alloc method for preview layer that may cause crash when releasing the object on iOS 7 (arm64).

[riza]

In 4909:

Re #1762: When capturing, image stride is not always equal to the image width. I.e on Ipad air, at 352*288 the image stride is 384. Additional discard process is
needed to correct the image rendered.