Make pattern detection symmetric

[fedarko]

After identifying a pattern, check:

• Is this pattern palindromic? (That is, does it contain a node A and a node -A?) If so, stop here.

• Do distinct reverse-complementary versions of the pattern's nodes and edges exist? For example, if this is a bubble containing nodes 1, -2, 3, and 4, do nodes -1, 2, -3, and -4 also exist in the graph? If not, stop here.

If both of these criteria are met, then we can create a new reverse-complementary version of this pattern along with the first one. This ensures that pattern detection is symmetric.