Update Installing.md

Add step 2b that references Header Search Paths that were seen in this GitHub issue:
https://github.com/wix/react-native-navigation/issues/1933

V1 had two SideMenu implementations. In v2 we've decided to stick with one and for some reason
code related to the unsupported implementation was left in the project.

This approach is still not ideal as it assumes there's a visible stack somewhere in the Hierarchy.
It's better than the current implementation so I'm pushing it and will reiterate in the future if needed.

This effectively reverts 96661e3308 and fixes the issue properly.

custom component.

* Fixed constants bug (closes #4807)

* Fixed constants bug (closes #4807)

Corrected 

Controls he behavior of screens displayed modally. 

to this

Controls the behavior of screens displayed modally.

Closes  #4001

Useful for aligning the title when TopBar height is changed.

Closes #5157

This is an example of how to use React’s Context API and RNN. This solution isn’t ideal, hopefully someone
would be able to build upon this example and improve it.

When a Stack’s root was set with an id of one of the Stack’s current children, there was a crash
since the wrong elements were removed from the stack.

This commit fixes this by creating a new stack when setStackRoot is called, and destroying all ViewControllers from the previous Stack.

Fixes #5117

Fixed minor linguistic mistake

Pass component passProps to componentDidAppear event

When setting left button and the title was centred, it got an undesired offset.
Now whenever left button is set we make sure to realign the title.

When a topBar.backgroundComponent is defined, check if a corresponding ReactView has already been created with matching componentName and componentId. If such view is found, reuse it instead of creating another view.

This change will fix a flickering in the TopBar background component when a screen was pushed into a stack with a background component.

After migrating to RN 0.59, view creation timings have changed a bit.
Seems like ruining this logic on pre draw sorts things out.

Fixes #5124

When mergeOptions was called on a root view, it’s one time options weren’t cleared properly.
The entire one time options logic is terrible and has to be refactored out.

Fixes #5010