Algebra subgraph submission

[cauu]

Here is my submission, please take a look:
https://github.com/cauu/algebra-subgraph-migration

There are two major problems that I've met:

1. The sync speed is not as fast as expect, it takes around 1 hour to sync a block; I've tried batchInsert method, but it didn't help(Not sure whether I use it wrong); Right now, i just add an indicator, so you can see the handling progress;
2. The bigDecimalExponated method is very slow especially when there's a large exponential power value;

If you have any advice on those questions, please let me know, , Thanks!