Adds CustomFontTextView to use fonts not supported in older versions

(like Roboto Thin)
Do not crash if we can't find any content as text

This fixes a crash when the content is null and we try to parse that into HTML
Adds pagination to the feed of news (triggered when scrolling down)
Uses Activity as mediator between TaskFragment and other fragments
Merge branch 'master' of github.com:xrigau/hn-android-client