Allows for larger data columns (totalling about 2mb in size)

This PR primarily does 2 things:

1.  Expands the text columns in wallets to MEDIUMTEXT types (with a max size of ~16mb)
2.  Updates stex to allow customization of the body size limit within express
3.  Sets that limit to 2mb.

This should give us quite a lot of headroom for people with lots of contacts.