[Applications][Linux] Remove unused variables from xwalkctl
[Applications][Tizen] Fix having to export the HOME variable for user 'app'

When the user changes to the 'app' user (e.g. using 'su - app') the
HOME environment variable is not set by default, this variable is used
for finding the address of the D-Bus session bus.

This is separated in a different header so it can be used by other tools,
see later commits.
[Applications][Linux] Add a tool to launch applications

This tool will launch an Application using its AppID (either via
parameter or via argv[0]).  It will talk to Crosswalk using the
'org.crosswalkproject.Running.Manager' and
org.crosswalkproject.Running.Application' to run and follow the
Application lifetime.

On Tizen, this tool will use the appcode infrastructure to get more
information about the launched application state.

We re-use the functionality of setting the 'HOME' environment
variable that was introduced in the previous commit.

And to avoid polluting the main binary with #ifdef's we put
the platform specific code (dealing with Tizen's appcore) into
a separated header.
Merge pull request #1346 from vcgomes/xwalk-launcher-tool

[Application][Linux] Add a tool to launch applications