[NUI] VisualMap, friend assembly, InputMethodContext related changes (#406)

[NUI] VisualMap, friend assembly, InputMethodContext related changes (#406)

* [NUI] Add DestroyContext call before disposing TextField/TextEditor

In order to speed up IME hide, temporarily add DestroyContext call.

Change-Id: Id93c99f4d45061d4e406d36ced7a0ec09c8f2c34

* [NUI] VisualMap revising

Here are some changes:
Add VisualFittingMode property
Add Atlasing property
Add Shadow,Underline,Outline,Background property
Add RenderIfTransparent property

Change-Id: I8d85f9d1a438cb6fbb636f79c7438e9134e1df8f

* [NUI] Add visual test example

Change-Id: I25f41d969f7b98a494a4fa1716b0335c09ab5026

* [NUI] Add friend assembly for Tizen.TV.NUI.Component

Change-Id: I2fdc02205c03aa98260035fb81998d68514c030e