Fix event filters (#41), lastTransitionTime not updated in conditions, and path finalize

[phlg]

This started as a PR to fix #41 (through a rollback of the changes to event filtering introduced in v0.8.0), but has some extras :

• Does away with meta.SetStatusCondition(), as the way we use conditions in this operator does not fit well with the way that function works (mostly, it doesn't update lastTransitionTime if a new generation of CR implies re-obtaining a condition that the CR was previously in). We did this in a basic & naive implementation in a separate utils.go created for the occasion. Can probably be upgraded.
• The recently added Finalizer management did not work well for paths. If a Path CR was created with a wrong spec (eg : on a non-existing bucket), then then actual path does not exist on the S3 backend, and the finalizePath() function chokes on this. It was reworked to actively check for path existence prior to attempting deletion.