Error with deleting fit that was once used as a command fit

[blitzmann]

1. Add fit A to fit B as a command fit.
2. Remove Fit A from Fit B
3. Attempt to delete Fit A
4. Error:

Traceback (most recent call last):
  File "C:\Users\holme\Documents\Sync\Git\blitzmann\Pyfa\gui\builtinShipBrowser\sfBrowserItem.py", line 333, in OnLeftUp
    btn.DoCallback()
  File "C:\Users\holme\Documents\Sync\Git\blitzmann\Pyfa\gui\builtinShipBrowser\sfBrowserItem.py", line 50, in DoCallback
    self.callback()
  File "C:\Users\holme\Documents\Sync\Git\blitzmann\Pyfa\gui\builtinShipBrowser\fitItem.py", line 373, in deleteBtnCB
    self.deleteFit()
  File "C:\Users\holme\Documents\Sync\Git\blitzmann\Pyfa\gui\builtinShipBrowser\fitItem.py", line 391, in deleteFit
    sFit.deleteFit(self.fitID)
  File "C:\Users\holme\Documents\Sync\Git\blitzmann\Pyfa\service\fit.py", line 211, in deleteFit
    if booster.boosted_fit != fit and booster.boosted_fit in eos.db.saveddata_session:  # GH issue #359
  File "C:\Users\holme\Documents\Sync\Git\blitzmann\Pyfa\venv\lib\site-packages\sqlalchemy\orm\session.py", line 2123, in __contains__
    raise exc.UnmappedInstanceError(instance)
sqlalchemy.orm.exc.UnmappedInstanceError: Class 'builtins.NoneType' is not mapped

This has to do with this tacky code:

    @staticmethod
    def deleteFit(fitID):
        fit = eos.db.getFit(fitID)
        pyfalog.debug("Fit::deleteFit - Deleting fit: {}", fit)

        # refresh any fits this fit is projected onto. Otherwise, if we have
        # already loaded those fits, they will not reflect the changes

        # A note on refreshFits: we collect the target fits in a set because
        # if a target fit has the same fit for both projected and command,
        # it will be refreshed first during the projected loop and throw an
        # error during the command loop
        refreshFits = set()
        for projection in list(fit.projectedOnto.values()):
            if projection.victim_fit != fit and projection.victim_fit in eos.db.saveddata_session:  # GH issue #359
                refreshFits.add(projection.victim_fit)

        for booster in list(fit.boostedOnto.values()):
            if booster.boosted_fit != fit and booster.boosted_fit in eos.db.saveddata_session:  # GH issue #359
                refreshFits.add(booster.boosted_fit)

        eos.db.remove(fit)

        pyfalog.debug("    Need to refresh {} fits: {}", len(refreshFits), refreshFits)
        for fit in refreshFits:
            eos.db.saveddata_session.refresh(fit)

        eos.db.saveddata_session.commit()

I am still working on #1524 on/off, which let me to this issue. I hope to delve into it with this work, as I'm reworking a lot of old functionality. Keeping track of it here though for now, but if anyone is interested in taking a look into this, feel free to submit a PR - the deleteFit functionality is probably not going to be changing drastically from my work.