Feature/12 adding tags to dataset in prep behaves inconsistently

Most issues listed in #12 (closed) are fixed already.

Fixes:

• "pressing enter in input field reloads page instead of saving" by using bootstraps own mechanism trough transforming the save-button into a proper form submit
• "country tags miss input field" by distinguishing more cleary between countrys (controlled vocabulary, limited to post-soviet area countries) and the user generated tags

Fixes #12 (closed)