added new version of openproject-icon-font

- uses only unpronounceable unicode chars
- more icons
- adapted all icons to new unpronounceable unicode chars
Improved usage of icon font

- added data-icon css rules to the icon classes
- replaced all 'data-icon' occurrence with the css classes
Icons for the content area

- started to use the icon font in the content area
Use new delete icon

- removed old delete icon styles
- uses new icon font for delete icon
- whitespace fixes in app/views/projects/settings/_versions.html.erb