Support cmd-a, c, v, x for text input in native dialogs like file open, save

[anirudhsasikumar]

Addresses this bug:

1. File -> Open.
2. Type in some text in the file open dialog (in the search field in Yosemite or filename text input)

Actual: Try Cmd-A, C, X, V - they do not work.
Expected: They work.

[peterflynn]

Awesome! Fixes adobe/brackets#4561.

[RaymondLim]

@anirudhsasikumar Nice work! I did try it and discover that we also need to implement for undo and redo in these input field. Can you add Cmd-Z and Cmd-Shift-Z in your implementation?

[RaymondLim]

@anirudhsasikumar I think this implementation is causing an undesirable side effect; when pasting something in the editor window, we're getting the double pasting of the clipboard.

[anirudhsasikumar]

@RaymondLim Ah - then the check:

if ([[self mainWindow] firstResponder] == [self mainWindow]) {

Needs to be applied not just for select all, but for copy/cut/paste as well. I'm guessing code mirror is handling paste by itself (without the actual paste command firing).

[anirudhsasikumar]

I will double check and update this pull.

[anirudhsasikumar]

@RaymondLim Please take a look now, the selectors will only fire when CEF isn't in focus.

[RaymondLim]

It's ok to have Cmd-Y for redo, but most mac apps provide Cmd-Shift-Z as redo. So we also need to handle that.

[anirudhsasikumar]

Fixed - only using Command-Shift-Z for redo now.

[RaymondLim]

Looks good! Merging now.