Multiway join rules

Add rules to compile query to a plan using HyperCube shuffle and multiway join. 
* [x]  add rule to merge left deep join into nary join in logical plan
* [x]  add rule break nary join to hypercube shuffle and local multiway join
* [x]  add rule to instantiate local multiway join (currently we only have leapfrog, but there could be more, so this part is seperated from break break nary join)
* [x]  add rule to place sort before LeapFrogJoin.
* [x]  add unit test
* [x]  add query test
 

Yick -- I don't like the inline `\` nor the inline `x if blah else y`.

```python
if self.multiway_join:
    target_phys_algebra = MyriaHyperCubeAlgebra(self.catalog)
else:
    target_phys_algebra = MyriaLeftDeepTreeAlgebra()
```