Add explicit support for ChromeOS and Linux

[mohnish]

Refer: https://developer.chrome.com/apps/commands

For the suggested_key key,

// left
"suggested_key": {
  "default": "Shift+Alt+Left",
  "windows": "Shift+Alt+Left",
  "mac": "MacCtrl+Shift+Left",
  "chromeos": "Shift+Alt+Left",
  "linux": "Shift+Alt+Left"
}

// right
"suggested_key": {
  "default": "Shift+Alt+Right",
  "windows": "Shift+Alt+Right",
  "mac": "MacCtrl+Shift+Right",
  "chromeos": "Shift+Alt+Right",
  "linux": "Shift+Alt+Right"
}

[xxKeith20xx]

Alt+Shift+Left/Right works great in ChromeOS 68 but can't assign the up and down arrows with alt+shift.

[defel]

Under Linux it is build-in since ever (and I alway hated it that it dont works on OSX or Windows)

Shortcut is: Ctrl+Shift+PageUp and Ctrl+Shift+PageDown