Linux Mint 18.1 is based on Ubuntu 16.04 which is currently not supported because of PHP 7. Please switch to another GNU/Linux distribution or just wait for i-doit 1.9. The pro version will be published in May.
in the Open version it's not possible to change the objecttype groups within the GUI.
In the Pro version you have a tool called Quick Configuration Wizard that allows you to edit them.
What you can do is edit the database. The list of groups is in table "isys_obj_type_group". Just add your own group there (ID above 1000) and make sure all columns are filled (Just make it match the existing ones).
Add the LC (Language constant) you created to a custom language file. An example can be found at /src/lang/de_custom.example.inc.php. More information here: Knowledgebase
Thanks for your request. There is an easy way to connect one input with two or more outputs: Just create one input (with no connected output) and then two outputs connected to the input. You will get a similar result as in the online demo for i-doit pro.
The other way (two inputs connected to one output) is currently not possible with i-doit pro. Can you give us a simple drawing which scenario in real life you would like to document? Maybe there is a workaround.
I figured it out. Our i-doit instance is set to require authentication from JSON-RPC calls, which are not included in the JS files in the module. I unchecked this option and it works. As this is a test environment this is fine for now, but I may need to hard-code authentication at a later date when we move into production.