Changed Printer rendering from character based to AttributedStrings

One drawback of the original printing system is, that every character is printed separately. 
As noted in the source comments, kerning and ligatures are not possible. Another nasty thing is, that underlines are dashed (see the attachments 'original' and 'after'. 


Technically I Made a character line puffer with an NSMutablaeAttributedString, every time a line feed or a horizontal or vertical  Head moves, the line puffer will be rendered to the view, and a new line buffer is started. 



Things still ToDo:  
I decided to move the default font from "Roman" to "Helvetica" since this looks more modern on printings. A settings dialog to let the user choose which default font to use would be nice. 

In the "original" attachment you can see that the colons (:) in the bill are nicely in one column. I didn't get it in the new printing that they are nicey one under the other. 

The kerning - Old printer have the CPI setting - a nice way to convert the CPI to a meaningful kerning value should be found. 

I have only one dos application that needs to print bills, I can not test this with other apps and can not test it with images etc. Hope that pull request will help to get a full useable dos printing. 

Regards
VVAanchesa


![teamworker_original](https://cloud.githubusercontent.com/assets/501326/4086906/2c2119ec-2f42-11e4-8ed3-eede96f3d6b7.png)
![teamworker_withkerning](https://cloud.githubusercontent.com/assets/501326/4086907/2c4218c2-2f42-11e4-91ec-b8a3135ecdcf.png)