Issue #404 - Create common library shared between plugin/engine and installer

common/common.gypi

 # This file is part of Adblock Plus <https://adblockplus.org/>,
 # Copyright (C) 2006-2015 Eyeo GmbH
 #
 # Adblock Plus is free software: you can redistribute it and/or modify
 # it under the terms of the GNU General Public License version 3 as
 # published by the Free Software Foundation.
 #
 # Adblock Plus is distributed in the hope that it will be useful,
 # but WITHOUT ANY WARRANTY; without even the implied warranty of
 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
@@ skipping 32 matching lines @@
       'sources': [
         'test/RegistryTest.cpp',
         'test/IeVersionTest.cpp',
       ],
       'defines': ['WINVER=0x0501'],
       'link_settings': {
         'libraries': ['-ladvapi32', '-lshell32', '-lole32'],
       },
       'msvs_settings': {
         'VCLinkerTool': {
-          'SubSystem': '1',   # Console

[Oleksandr, 2015/03/04 05:26:29]

Nit: No space after #

[sergei, 2015/03/04 08:02:00]

Did you mean "one space before #"? Actually, as I see, we use space after #. But
we usually put comments in gyp files on a separate line before the commented
line.

[Eric, 2015/03/04 14:15:16]

This 'msvs_settings' section is copypasta from the main GYP file
'adblockplus.gyp', where it appears twice.

Is there a need to change this, really?

[Oleksandr, 2015/03/04 15:37:23]

Yes, I actually was meant to say one space _before_ #, sorry. This can be fixed
in adblockplus.gyp sometime later as well. 

[Eric, 2015/03/04 16:55:10]

I fixed all of them. We're already altering adblockplus.gyp; no reason not to do
it now.

+          'SubSystem': '1', # Console
           'EntryPointSymbol': 'mainCRTStartup',
         },
       },
     },
   ]
 }