Update your-first-app.md to current API
Update your-first-app.md to current API

Use package.json instead of index.json, omit tabris.load.
Use backticks for technical names only, emphasis for UI elements.

Change-Id: I20f3e26f4fe3d915b2641538f603ee755ff23651

moham3d/tabris-js,mkostikov/tabris-js,eclipsesource/tabris-js,pimaxdev/tabris,mkostikov/tabris-js,softnep0531/tabrisjs,softnep0531/tabrisjs,pimaxdev/tabris,eclipsesource/tabris-js,eclipsesource/tabris-js,moham3d/tabris-js