Add the option to hide camera preview on startCamera

[jbotte]

I noticed that CameraPreview.startCamera is slow, to combat this I start the camera during app startup, then I hide the camera. This creates a quick little flash (the design of my app doesn't work with toBack:true.

I already have a version in the works on iOS it seems to pass testing.

If a user adds the param hideOnStart : true to their startCamera Options the camera hides. the general CameraPreview.show() seems to work fine bringing it back into frame.

On android I have the camera hiding but the CameraPreview.show() doesn't bring the preview back up, I have to force some sort of screen redraw by manually opening up the app switcher then clicking back on the app.

I would love someone to help me get these changes over the line as a potential feature to add. I don't have any real android Java experience or I would most likely have figured out the issue.

Here is a link to my repo, you should only really see one commit with the changes (aside from readme notes)

https://github.com/jbotte/cordova-plugin-camera-preview