[Tizen] Move platform sensor initialization out from browser UI thread.

Cold start time of sample Calulator application increases to ~1080 ms on
Tizen VTC-1010 at the moment. One bottleneck is it takes long period to
initalize platform sensors inside browser main thread, which blocks native
window display and starting render message loop.

The CL moves the platform sensors initialization outside of browser main
thread. The local test result shows it shortens ~200ms of cold start
time.

BUG=XWALK-2520
[Tizen] New discovery page for devtools.

Add chrome style decorates to discovery page of devtools to improve user experience.

BUG=https://crosswalk-project.org/jira/browse/XWALK-2525
[Tizen] No need to show crosswalk icon
The icon of crosswalk is shown on ivi-ux-ico which is not correct.
This fix modifies the crosswalk config file to not show its icon by default.

BUT=TC-1708
Merge pull request #2497 from yejingfu/bug-fix

[Tizen] No need to show crosswalk icon on ivi-ux-ico
Merge pull request #2409 from iKevinHan/new-devtools-page

[Tizen] New discovery page for devtools
Merge pull request #2460 from shaochangbin/sensor-launch-time

[Tizen] Move platform sensor initialization out from browser UI thread.