Implement WriteLock for VolumeDataLayer to avoid errors with multiple VolumeDataPageAccessors

• Add option to WriteLock VolumeDataLayers in order to check that we don't create multiple VolumeDataPageAccessors for layers while writing data.
• Add code to VolumeDataPageAccessor to acquire the VolumeDataLayer WriteLock in CreatePage()/GetWritableBuffer() and release it in Commit().
• Add check for write-locked layers in HueVolumeDataPageAccessor_c::ReadPage and throw exception if reading from another accessor than the one that has the write lock.