Add missing images and demos

Closes #124.
Merge branch 'master' of github.com:operasoftware/devopera

* 'master' of github.com:operasoftware/devopera:
  Updated pictures
  Links added
Add missing files

Fixes #125.
Fix typo in `showModalDialog` demo

Hat tip: @zcorpan.
Avoid minifying demo HTML files

Closes #129.
Merge branch 'master' of https://github.com/operasoftware/devopera