Adding Marketing/Tracking functions

Added support:
- more than one Short-URL with the same target URL (not unique anymore)
- Integration of a simple counter for each short url
- Comment-Field for each short url
- Bug (?):When editing an existing short-url avoid creating a new short-key
- Introduced a new marker "marketing" - because when using the typolink-function for an already existing target url this is only used when the target is not an marketing url.

Description of Marketing:
- The idea is to create short-URLs for different media - example: flyer, newsletter, v-card, and so on. 
- Each of the media should be counted seperately
- This "marketing"-Short-URLs should not overlap with URLs created by typolink, because the a typolink should not be counted on a markteing url and vice versa.

The "Markeing" functionalty is complety compatible with the original version of tinyurl (0.1.0).