Add script for checking coding style

Uses cpplint.py from Chromium depot_tools. Since we all have depot_tools
to build Crosswalk, it is OK to depending on it.

For now all the directories are ignored so we can fix things gradually.
Fix common/ coding style
Fix notification/ coding style
Fix power/ coding style
Fix time/ coding style
Fix network_bearer_selection/ coding style
Fix tizen/ coding style
Add exception for system_info/

SystemInfo makes use of non-const references in its code. Add a filter
to ignore this for now.
[demo] add system info demo

The added demo packages is:
   tizen-extensions-crosswalk-system-info-demo-${version}-${release}.${arch}.rpm
Install the package with `pkgcmd`, like:
   $ pkgcmd -i -t rpm -p tizen-extensions-crosswalk-system-info-demo-0.2-0.i586.rpm -q
More information about demos at commit `1ed2d38`.
[download] Fix bug which stops download being able to build for mobile
[SystemInfo] Support read-only properties
Merge pull request #117 from legendlee1314/master

[SystemInfo] Support read-only properties
[SystemInfo] Fix running error on system_info.js
Merge pull request #119 from legendlee1314/upstream_master

[SystemInfo] Fix running error on system_info.js
Merge pull request #115 from deqing/master

[download] Fix bug which stops download being able to build for mobile
Merge pull request #110 from cmarcelo/check-coding-style-script

Check coding style script
Use new Crosswalk Extension C API

This commit changed ExtensionAdapater to use new Extension API without
changing any of the existing Context classes. That said,
ExtensionAdapter could be rewrote now with less templates and in a more
straightforward way.
Remove --fullscreen from tizen-extensions-crosswalk script.

We don't need to call --fullscreen, Xwalk can figure out by itself
that it should run in fullscreen or not as we integrate with the
window manager.
Merge pull request #120 from darktears/fullscreen-fix

Remove --fullscreen from tizen-extensions-crosswalk script.
Merge pull request #106 from cmarcelo/c-api

Use new Crosswalk Extension C API