[Runtime] Move "is_running_as_service" flag to XWalkRunner

This distinction will be used later in xwalk_paths, to setup different
data paths for Crosswalk in Tizen.
[Runtime] Small refactor to our PathProvider

Move the logic for xwalk::DIR_DATA_PATH to a separate function, and
create a helper function for Linux for getting the config path from
XDG. These will be useful when we transition Tizen to use home directory
for service mode instead of the "/opt/usr/apps".
Merge pull request #1408 from cmarcelo/run-as-service-switch

[Runtime] Move "is_running_as_service" flag to XWalkRunner
Revert "[Tizen]Remove the openssl BuildRequires"

The code in crypto/crypto.gyp only pulls in the dependency on
third_party/openssl when building for Android.

For now, revert the commit as it was not essential while we can fix this
upstream.

This reverts commit f8d9749eb4320d49527184214df1d028e242d7b7.
Merge pull request #1410 from rakuco/revert-pr1394

Revert "[Tizen]Remove the openssl BuildRequires"
Prepare ApplicationService for multiple applications handling.

Prepare ApplicationService for multiple applications handling: ApplicationService now owns a ScopedVector of Applications.
Application::Observer class is introduced so that application can notify about its termination and deletion.
Application::Launch methods return a pointer to the corresponding Application instance, ApplicationSystem methods are modified accordingly.
[Application][Linux] Remove unused CommandLine
Merge pull request #1411 from cmarcelo/remove-unused

[Application][Linux] Remove unused CommandLine
Merge pull request #1409 from cmarcelo/small-refactor-xwalk-paths

[Runtime] Small refactor to our PathProvider
Merge pull request #1388 from pozdnyakov/Prepare_for_multi_app

Prepare ApplicationService for multiple applications handling.
[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. Currently we don't really know what
dependencies we are getting for free from xwalk.gyp which is getting bloater and
bloater.
[SysApps] Make a self contained module out of sysapps.gypi

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

Include this file other than src/build/filename_rules.gypi if you have files
suffixed with _tizen or tizen/ directories. For now on, let's stop using
conditionals for source code in our build system.
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.
extensions
extensions
test_base
test_base