Add camera toggle button to enable/disable camera

[wisechengyi]

PR for #14

Other changes:

• memoized device window, so MainGUI does not have construct a new one every time.
• Proactively trigger refreshDevicesIcon on camera change events.

[apockill]

Hi Yi,

I have a couple things I would like you to address before I pull this into the main repository:

• Naming conventions: Please make sure that the new functions you add use camelCase, not snakeCase. I know that pep8 specifies snakecase, but since the entire project is camelCase it seems a bit out of place. Examples: get_toggle_button_text()
• I know that memoizing functions can be useful for optimization. But I don't think that a small utility function like this needs that, and since it involves adding a whole module to the project, I would rather avoid doing that. Could you change your implimentation so that it doesn't use util.py, or memoization?

I think that's it. Other than that, it looks good!

[wisechengyi]

Addressed all comments. Should be good now. Thanks, Yi

[wisechengyi]

@apockill btw are you working in shenzhen now?

[wisechengyi]

ping

[apockill]

Hi Yi, sorry about the delay, it's been a busy few days. I'm actually studying in Arizona right now.

Anyways, looks good! I'll pull it in.

[wisechengyi]

@apockill when you merge, you probably want to use the squash option on github. Otherwise a lot my meaningless commit messages will show up on master :P