* Add font family support on bottom tabs

* import missing classes

* import missing class

* update document

* Save titleBarHidden in screenParams when toggling TitleBar

* empty commit

Closes #681

collapsingToolBarExpendedColor - determines the TitleBar color in expended mode
showTitleWhenExpended - defaults to true when expended color is defined.

Implement backgroundColor and textColor style params

This commit contains various fixes and enhancements, mostly because I
was too lazy to commit small changes.

* Add topBarCollapseOnScroll style property which compliments
  navBarHideOnScroll. This property is needed when showing a
  collapsing topTabs screen. In this case the developer might to keep
  the titleBar bar when the screen is collapsed.
* Reduce collapse sensitivity by taking scaled touch slop into account
* Cancel touches when collapsing. This fix prevents buttons from
  responding to touch events when collapse ends.

This commit adds support for icons in TopTabs.
It’s possible to have icons with text, or only icons.
Use topTabIconColor and selectedTopTabIconColor to color the icons

related to #557 #474 #125

closes #454

* Implement screenBackgroundColor

* Collapse ViewPagerScreen on TopTab select

* Move event emmiter logic out of Application

* Implement searchView

Usage:
```js
rightButtons: [
      {
        id: 'searchView',
        label: 'Search',
        hint: 'Search...'
      }
    ]
```

* Translucent TitleBar

* Collapse TopBar

* Less noticeable translucent effect

* Implement ScrollViewDetector

* Collapse on fling

* Collapse on touch up

Complete collapse on touch up instead of fling

This change means that in a tab based app, when pushing a screen
which did not declare `tabBarBackgroundColor` - the BottomTabs color
will persist from the previous screen and not be set to the default
color which is white. This eliminates the unwanted BottomTabs
background color change in this specific use case.

closes #409

Can also be set cross app by using titleBarDisabledButtonColor property in appStyle