Make test base a self contained library

So browsertests binaries can link with it. Previously it was part of the main
xwalk_browsertest and had the assumption of a single test runner.

The ideia is to split the browsertests by components, making the faster to run
and also helping to keep track of dependencies.
[Extensions] Buildsystem refactoring

The main point of this patch is to move build units from "includes" to self
contained modules. The reasons are:

- Includes have their path relative to the file which includes the .gypi. So if
another component not located at the root of xwalk depends on extensions
(sysapps for example), it won't work.

- Make it easier to track dependencies. Instead of adding all the dependencies
inside xwalk.gyp, we isolate them to the component that requires it.

- Have separated test runners for extensions, making run tests faster.
[SysApps] Buildsystem refactoring

For the same reasons stated in the previous patch refactoring the
extensions buildsystem.
Add filtering rules for Tizen

Filter files suffixed with _tizen or tizen/ directories, depending on
whenever 'tizen' or 'tizen_mobile' is set.For now on, let's stop using
conditionals for source code in our build system.

The rules will automatically apply to every project file, because common.gypi is
included by gyp_xwalk script.
Remove platform conditionals for source code

Now that we have file filter rules for Tizen, we don't need to use conditionals
on the build system for source code we own.
Disable gyp's circular reference checking for Mac

We have now a few false positives because the browser tests depends
on the runtime target which is currently declared in xwalk.gyp which
includes xwalk_tests.gypi which depends on the browser tests.

The target relationship is not circular, but the file references are.
[Extensions] Make the browsertests build on Mac

Fix all the nits that are making clang sad.
[Extensions] Make Mac build the external extensions samples

Do not strip the binaries because Mac tools don't like when you
change the default 'product_dir'.
Remove a platform conditional build

Using file suffixes instead.
Ident xwalk_tests.gypi properly
[Dialog] Make it a separated module
Merge pull request #1387 from tmpsantos/build_system

Build system refactoring