Make the mouse context menu configurable

[GoogleCodeExporter]

The right-click context menu should be able to be both disabled and configured.

One way of doing this would be to add a section in the settings file  
specifically devoted to what is available in the right click menu.  It could 
look like this:

    "context_menu": {
        "enabled": "true",
        "show_print": "true",
        "show_back": "true",
        "show_forward": "true",
        "show_save_as": "false",
        "show_copy_link_address": "false",
        "show_copy": "true",
        "show_cut": "true",
        "show_paste": "true",
        "show_inspect_element": "false",
        "show_view_source": "false"
    }

Some of these features might be best to leave out (such as copy and paste) but 
were included in this list to be complete.  

It would be nice if it would only show the context menu if there was an action 
to take that was enabled in the settings.  For example, if you right click on 
the page, there would be no context menu, but if you highlight text and right 
click it, a context menu would still appear with copy, cut, and paste.

Original issue reported on code.google.com by [email protected] on 24 Jan 2014 at 12:15