OK guys, thank you for your help. I haven't heared of those 2 programs before, but they definitely go in the right direction. However, the codes used to generate those images seem kind of ugly to me - too many redundant loops and all that, which is why I wanted to use something like Scala to begin with.
Luckily I found a solution - not a great one, but it works. My "IDE" consists of two components now, a small window I created with DBPro, and Notepad++ as the code editor.
Right now (in its pretty unfinished but kind of working form) it looks like this:
When I click on one of the Files in the list on the left side, DBPro will execute the respective text file, which leads to Notepad++ opening it in a new tab automatically. When I press the Build or Run-Button on the left side, DBPro creates a batch-file that contains the scala compile and execute instructions required to compile and run the selected scala file. Finally, the output of scala editor and interpreter are printed to the small window in the lower left corner (and still have to be formatted properly).
After running a code, the image in the upper left corner is automatically updated by reading it from the hard disk, which obviously only works when the scala-code exports an output image beforehand, which happens in line 41 in the screenshot.
Well, this is not a WIP post or anything, I just thought somebody might be interested in my solution.
Thank you and have a nice day!