Add XW_Extension_EntryPoints.h

This defines an internal interface in Crosswalk to setup "entry points"
of the API, so that Crosswalk can load the JS API on demand.

For example, 'tizen.time' will be loaded when the web content tries to
access 'tizen.time' in JS, but also when the web content tries to access
'tizen.TZDate'. This extra symbols are the entry points.
Add entry point information for extensions using new C++ wrapper

Entry point information is used by Crosswalk to know what symbols
can trigger the load of the extension, in case it decides to load on
demand. The extension name is implicitly an entry point, so we just
set the extra entry points.

This should cause no changes if the Crosswalk doesn't support the
interface for setting entry points yet -- like Crosswalk 1.
Add entry point information for extensions using old adapter

Entry point information is used by Crosswalk to know what symbols
can trigger the load of the extension, in case it decides to load on
demand. The extension name is implicitly an entry point, so we just
set the extra entry points.

This should cause no changes if the Crosswalk doesn't support the
interface for setting entry points yet -- like Crosswalk 1.
Merge pull request #219 from cmarcelo/entry-points

Add entry point information for extensions