Add in UefiApplicationEntryPoint library class and library instance.

Add in UefiApplicationEntryPoint library class and library instance.
The major difference between UefiApplicationEntryPoint and UefiDriverEntryPoint is that:
1) UEFI application will always be unloaded no matter what is the return status code from the application. Therefore, the library destructors should be called always.
2) UEFI application should not register any callback to evevnt such as EFI_EVENT_GROUP_VIRTUAL_ADDRESS_CHANGE and EFI_EVENT_GROUP_EXIT_BOOT_SERVICES.
3) UEFI application does not support module merger like Uefi Driver.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@2199 6f19259b-4bc3-4df7-8a09-765794883524