Fix crash when editing transform mask too actively

1) Now KisSpontaneousJob has an 'exclusive' property, which guarantees
   that now other update jobs are not running in parallel

2) KisModifyTransformMaskCommand mush not call m_mask->recaclulateStaticImage()
   directly, it doesn't guarantee exclusive access to a paint device, which
   can cause a crash (because the transform worker calls KisPaintDevice::purge(),
   which demands exclusive access).

BUG:395224