Handling file opening (#329)

* Add function to escape a shell argument.

* Keep track of the last used window.

* Implement support for the open-file event.

* The shell escape regex needs parentheses to be captured.

* Removed lastWindow and added getLastFocusedWindow method to app

* Create window create new session only if no callback passed

* Added app.windowCallback to handle open-file before "ready"

* Small lint fixes

* Differeent open file handling: check if it is directory, and if the file is executale or not

* Small fixed and added some comments

* Added php-escape-shell module in place of custom escapeShellArgument()

* Fixed wrong code and added detailed comment

* Aliased php_escapeshellcmd import

* Rebased; added error handling in OpenFile

* changed string contatenation with template literal

* Pinned php-escape-shell dependency

* Typo fix

* getLastdFocusedWindow now uses Array.prototype.reduce()

* Notify users of unexisting path while open file

package.json

@@ -18,6 +18,7 @@
     "mousetrap": "1.6.0",
     "ms": "0.7.1",
     "object-values": "1.0.0",
+    "php-escape-shell": "1.0.0",
     "react": "15.3.0",
     "react-addons-pure-render-mixin": "15.3.0",
     "react-deep-force-update": "2.0.1",