[compiler] --python-package is not applied to relative imports / imported file is compiled into wrong directory
**Showcase:**
This branch https://github.com/OK-DMR/dmr-kaitai/tree/kaitai-relative-imports-not-working
and this commit specifically https://github.com/OK-DMR/dmr-kaitai/commit/21a89704681182aad2a65dc00e4385da3662759a#

*Commit shows the result of adding relative import to existing .ksy and result in compiled .py files*

**Issue**:
  1. Missing `from okdmr.kaitai.hytera.link_control import LinkControl` from resulting `mmdvm2020.py`
  2. Imported file is compiled in current directory (but that is currently probably un-avoidable until #914 is addressed)

**Testing/Reproducing**:
  1. Change .ksy file
  2. Run `rebuild-all.sh` from root of the repository
  3. Observe in `git diff`

**What should happen instead**
  1. When resolving relative imports resulting package of imported file should be based on `--python-package` from original compiler command, which would result in correct import statement of imported
  2. Ideally the imported file would be compiled under relative directory, equal to `meta/imports`, and not in current directory  (in commit you can see the freshly created okdmr/kaitai/homebrew/link_control.py which should not even be there), and import should be correctly `from okdmr.kaitai.etsi.link_control import LinkControl` (even if existence of this package and file should be just assumed)