Ignore data changes from non-text entities in level diffs

It is possible for entities to be marked as changed in level diffs even when they haven't been changed at all. This is because their data attribute has been changed, which happens due to the bug with the in-game level editor where, upon saving, the data attributes of non-text entities are filled with random strings from memory. (It is assumed that this bug is fixed in 2.3.)

That bug results in the entity diffs of the 2.1 and 2.0 versions of A New Dimension being extremely noisy.

To fix this, just ignore data attribute changes if it comes from a non-text entity. Now the entity diffs of A New Dimension 2.1 and 2.0 are no longer filled with noise.