Mac OS X: Add missing standard app keyboard shortcuts

[joshgerdes]

Please add the standard app keyboard shortcuts for Mac.

Details found here:
https://support.apple.com/en-us/HT201236

Missing the following in v0.1.515:

• Command-A : Select All items.
• Command-F : Find: Open a Find window, or find items in a document.
• Command-M : Minimize the front window to the Dock.
• Command-N :New: Open an new document or window.
• Command-O : Open the selected item, or open a dialog to select a file to open.
• Command-P : Print the current document.
• Command-S : Save the current document.
• Command-W : Close the front window.

[stirno]

looks like our ctrl->command mapping isnt working properly on OSX. joy.

[pauljz]

These will mostly be fixed in 526. Unresolved:

• Command-F is broken right now because it crashes the editor due to a recent change, but otherwise will work fine.
• Command-W closes the window, but should just close tabs until you close the final tab. We're not getting keypress events for this or it'd be a trivial fix. Need to figure out why.
• Command-P is intentionally unimplemented. We probably won't support printing for a while.