[NUI] sync with csapi-nui tizen_4.0 branch

[NUI] sync with csapi-nui tizen_4.0 branch

- the following patches are already merged in csapi-nui tizen_4.0 branch
- [Tizen] Modified value type of native layout direction property (ChangeId: Ibe6afa9a44a93f1edc50e2413246a807aad90648)
- [Tizen] Review nui API cs files (ChangeId: I0ddfd58c32c23f8c40d19548ef763e2008222716)
- [Tizen] Adding Property Notification support (ChangeId: Iac5d5e7b6ced6df9d2b651d36559f223e5a06fdc)
- [Tizen] (Window) Added a method to window so that we can render once, even when paused (ChangeId: I80c996e893f07c0ef51c7ef6933ba1a6114e54cf)
- [Tizen] .NETCore2.0 upgrade (ChangeId: Ibf0992a682666897417878fa458fa6d0f45372b6)
- [Tizen] temporal API to make users use Container class (ChangeId: If574d1fe180f0de6197cdc6cbed05d99cfa92d24)
- [Tizen] Update NUISamples to support .netcore 2.0 (ChangeId: I3b5955022644c4cd6345bfd56591fa189b9cd8e6)
- [Tizen] nui_0.2.56 version release (ChangeId: I16a19195fc808503914050609b9dc32e317460b4)
- [4.0] Remove redundant delegates and functions (ChangeId: Idedac9b958ed8e809bbd4bfe94218bf63a5cf9c2)
- [Tizen] nui 0.2.56 version release (ChangeId: Id5861dc8f2f3616efa27c245b650de80d61ba7c4)
- [Tizen] save 800ms when changing to small letter (ChangeId: Idcef8108888f184cfb52955942ca94a186da645b)
- [Tizen] Add Interval property for Timer (ChangeId: I22f83894065752d245150cb1374f6f4f456aa312)

Change-Id: Iccbaec1f7a63c210eab90e95428106683d4dd536
Signed-off-by: dongsug.song <dongsug.song@samsung.com>