Fix most (I hope) instances of Unable to establish a connection with SafariDriver

Tested on:
* OSX 10.8.5
* OSX 10.10
* Win 7 Safari 5.1.7

Issues: #7933, #7963, #7974, 7801

Refactor how the extension installation happens by splitting the
installer into multiple Platform specific installers. If the installation
still fails, provide a much more detailed explanation as to why the failure
occurred and suggestions how to fix it.

Conflicts:
	java/client/src/org/openqa/selenium/safari/SafariExtensions.java