the project has source code in paths like:
tests/src/de/pokerth
src/chatcleaner
which should not be ignored. To fix this, a slash needs to be added in
front of the files that actually should be ignored.
While at it:
- pokerth_server does not need to be ignored (it's generated in `bin/`,
which is ignored already)
- ignore some project files (for the case Eclipse is used as IDE)
