[NUI] Add Horizontal/VerticalAlignment to LinearLayout

[NUI] Add Horizontal/VerticalAlignment to LinearLayout

Previously, LinearAlignment of LinearLayout could not support the
combination of horizontal and vertical alignments.
e.g. could not support CenterHorizontal with Bottom

Now, HorizontalAlignment and VerticalAlignment have been added to
support the combination of horizontal and vertical alignments.

To use the enum types Tizen.NUI.Horizontal/VerticalAlignment for
LinearLayout.Horizontal/VerticalAlignment, the documentation of
Tizen.NUI.Horizontal/VerticalAlignment has been updated.