Making WebViewNix scale its content properly

Now the Nix WebView is smart enough so it can find the proper
scale for its content when a page starts loading.
If the comming page is a result of a back/forward command, it just
keeps the scale untouched, letting the cached scale to be applied.
However, if the load is a standard load and fixed layout is being used,
it tries to apply a scale, in order to fit the contents properly

Reviewed by: Daker Fernandes Pinheiro
API: Exporting scaleToFitContents and getScaleToFitContents

New API functions exported to NIXView. They are needed to let
the WebView decide the proper scale of the view

Reviewed by: Hugo Parente Lima
MiniBrowser: Removing all scaleToFitContents burden out of MiniBrowser

This is a task now performed by WebViewNix.
Additionally, the MiniBrowser does not need to care about the
load type (back/forward/standard) anymore in order to decide when
to scale the page, because this behaviour is now controlled by
the WebViewNix as well

Reviewed by: Hugo Parente Lima