[sailfish-browser] Add DeclarativeWebPage containing all browser specific properties. Contributes to JB#17328

Task: https://github.com/sailfishos/sailfish-browser/issues/50
Merge pull request #58 from rainemak/webPage

[sailfish-browser] Add DeclarativeWebPage containing all browser specific properties
Change MozView id to webPage and WebView to webView
Merge pull request #59 from rainemak/task50

Update ids of WebView and WebPage to be more descriptive
[sailfish-browser] Move properties from TabModel to C++ side. Fixes JB#17328

This commit has the same renamings as https://github.com/sailfishos/sailfish-browser/pull/59.
That is just to avoid merge conflicts.