fix(core): tolerate unknown elements in the project file parser - #2274
zs-stpa:topic/stpa/core/tolerant-project-parser
- ProjectFileStorage no longer rejects unknown elements in omegat.project: one team member saving with a newer OmegaT (extended schema) locked every member on older versions out of the project with "Unable to read project file".
- Unknown elements are now ignored on read, matching how the other configuration files behave; known fields are unaffected (covered by new test).